Maximize Triad score for missions. Don't worry so much about cop rank.
Unlike your cop rank, you can only increase your Triad experience bar to earn additional Triad-based upgrades by filling your Triad score (denoted by red triangles) during missions. Your cop rank, on the other hand, can be filled quickly and easily by completing tasks set out by Officer Teng. So don't worry if you inflict too much property damage while being chased by the cops, lowering your Cop score; there are other ways to build it.
By the end of the game, if you haven't reached Level 10 on the Triad bar (and want to reach it), you'll need to replay any missions you think you can improve on by entering the Social Hub.
To keep your Triad experience high during a mission, aim for headshots, damage vehicles before blowing them up, and mix up your attacks so that you aren't penalized heavily for repeating a move. Occasionally, you can delay certain parts of the mission by stalling the trigger for the next story scene and rack up Triad points slowly, say, by shooting enemy vehicles until kingdom come. But oftentimes you'll need to be fast, especially if you're in a mission where your allies can take out enemies while you're preoccupied.
If you have the Dim Mak counter earned by returning all of the jade statues, that's a good way to build the meter as well (+30 Triad points for each successful Dim Mak). Of course, you won't get every jade statue until you're late in the main story, so this is mainly for replays.
Focus on the knee stun combination first when upgrading melee.
Your kung fu sensei, who will be available after a main story mission in the early part of the game, can teach you additional moves provided that you give him one of the missing jade statues laying around the city. Many of them can be found just by noting their location during cut-scenes (also, note Tip #8). Once you find one, you can then trade it in for a new move.
I recommend obtaining the knee stun combination first. It might not look like much, especially since it's only upgrading your basic string of moves rather than adding an entirely new move. But the knee stun allows you to debilitate regular goons with ease, which gives more breathing room when you're facing off against seven enemies at once.
One branch beyond that is a boost that increases the string even further, so that Wei can knee stun and then kick an enemy in the face. This is really the move you want in your arsenal, since it takes weaker enemies out in one simple string, grapplers in two. Brawlers tend to block all strikes, so using the knee stun combination on them is a waste. Still, if you can take out the small fry out first, it leaves you much more room to deal with the tougher enemies.
Perform instant kills with environmental grapples and stuns.
The tutorial for environmental grapples and stuns comes early in the game, and their significance in combat can't be understated. Environmental grapples are one-hit kills, and once you upgrade the knee stun from Tip #2 or learn the leg break, a follow-up hit usually ends up in a one-hit kill as well.
The question then becomes when to use these powerful moves. Certainly, they're in your best interest if you just want to thin out a crowd. The brawler types, the ones that block the most, are among the best targets to take out with a leg break or environmental grapple. Suffice it to say, these are incredibly useful in martial arts clubs and enemy hideouts.
Where you might not want to use them is when you're trying to build your Triad experience, as explained in Tip #1. Environmental grapples only award 20 Triad points while the combo string for a stun follow-up is usually around 50 points. Still, Wei should be able to extract around 100 points per enemy using counters and a variety of moves. It may be a little more sinister for Wei to torture his victims like this, instead of ending it quickly, but when do players really care about the welfare of digital bad guys, right?
Sometimes defense is the best offense.
This may be counter-intuitive since the opposite is usually correct, but in this case, attacking too aggressively can get Wei killed. It only takes a handful of hits to send Wei ragdolling to the pavement, and getting interrupted by enemies can happen frequently if you're not careful.
Strong attacks leave Wei open to being countered by any of the enemies surrounding him, so it's usually better to fend them off by using grapples like the stunning leg break as well as stun follows-up, which tend to be resistant to being interrupted. But by and large, it's just as viable to hold back and anticipate an attack, leaving Wei open to counter at any time and from any angle.
I tend to use a string of quick attacks while looking out for the red outline of any foe so that I can make a quick counter. That way, Wei doesn't have to suffer too much damage and comfortably build his face meter for health recovery and unblockable attacks (available on the Face upgrade tree).
Pay for herbal teas, dragon kicks, pork buns, and messages.
Though the boosts from food, drink, and messages are temporary, and though mission failures reset boosts, they'll still a great idea. Early in the game, messages can be a bit pricey and you likely won't need them as much as you do the defense bonus from herbal teas, the attack bonus from dragon kick sodas, and the health regeneration bonus from food items.
But by the the middle of the game, you should have more than enough cash to get a boost for cheap while some of the more powerful moves and upgrades probably aren't available to you. This is the best time to go out of your way for a boost, but it's really up to you. The combat wasn't terribly hard for me, so I only looked for food and drink when it was on the way or close by anyway. Luckily, by the end-game, grabbing boosts are still worth their trouble since the face meter upgrades increase the effectiveness of food and drink.
Smash parking meters outside of missions.
Running into parking meters with a vehicle is a quick way to get cash early on. As long as you're not within view of the cops, you can earn about $500 every time you have time to smash through a string of meters. Sure, it's not a lot, but this quick bonus adds up quickly over the course of the game. This, along with finding a stray lockbox, is helpful near the beginning of the game when cash is harder to come by. Later on, it's far better to spend your time stealing cars and gambling to accumulate money.
If do you make this a habit, though, make sure you're in a vehicle since a motorcycle or scooter is usually too small to be precise enough to hit a meter. You also can't destroy meters with your fists or feet.
If all else fails, use a car as a weapon.
If you want to take down a group of thugs easily, almost too easily, just bring a car and mow them down one by one. As long as you're on the move, so that they can't throw you out of the car, you can run them over without batting a sweat.
Most of the time, though, cars aren't permitted since missions usually take place in buildings, warehouses, or docks. But it's still useful to remember that a car can be the best weapon when taking out a crowd of 16 or more thugs surrounding one of the more difficult gang hangout areas. Remember that you can also shoot a gun from your car too.
Dating will reveal the location of nearly all the collectibles.
Wei is a heartbreaker, dating women only once or twice before moving on to the next one. As much as he's a playa, though, it's to your benefit to score with all the chicks in the game, since doing so will reveal the location of hidden collectibles, including all of the jade statues, lockboxes, and health shrines. I wish there was one that showed all of the event locations, but I digress.
So in other words, don't bother trying to look for everything on your own. Explore a little bit and take the time to get a health shrine or lockbox if it's in your line of sight. But know that you can just go on every date and most of the collectibles will be open to you without you having to wander aimlessly around every alleyway.
For quick cash, find lockboxes. Later on, find marked cars.
Are you still hurting for cash at the beginning of the game? Just explore around North Point a bit and you'll inevitably run into one of forty lockboxes. Since they flicker brightly, they are hard to miss. There are even a few in the night market so you can open them easily for several thousand dollars.
Gambling on mahjong poker is also a safe bet, since the odds are in your favor. You won't be able to reach the gambling dens in the middle of the ocean until you have access to the favors that appear around them, so don't bother going there until then (unless you want to get a collectible).
Later in the game, the most effective way to earn cash is stealing cars, which you must earn the right to do by playing the main story up to the point when you first visit Central. All it takes is calling Tran, finding the marked vehicle (to speed things along, I like taking a taxi to a nearby parking garage around the vehicle), and then stashing it in one of Tran's garages. Make sure to stick with clean driving once you've got your hands on the marked vehicle since your pay will diminish with every ding and dent on it.
Stealing cars will reward you handsomely with tens of thousands (sometimes hundreds of thousands) of cash and, once you complete them all, you should have no trouble purchasing everything in the game and having a several million left over to spare.
Use taxis for instant transportation.
At first, I thought taxis were meaningless. Why pay for a slow taxi driver to take me to a place that I can easily drive to... perhaps by stealing the taxi itself? It wasn't until halfway through the game that I realized that the taxi provides instant transportation to any major location you wish to go. If I had known that sooner, it would saved me hours of unnecessary travel time, and so I impart this information to you so you don't make the same mistake.
Just make sure to hold down 'Y' (or triangle on PS3) while standing still to hail the taxi, or else Wei will attempt to steal the taxi instead. But there will be instances when there is no taxi around or when a taxi is driving away and Wei can do nothing about it. In these cases, I recommend stealing a car just to block the taxi (once you've found one), bringing it to a halt, just so you can use it... or just to be a dick.
A Big Betrayal - Complete Dockyard Heist.
A Slap in the Face - Kill someone with a fish.
Auto Enthusiast - Purchase all vehicles.
Big Smiles All Around - Complete Big Smile Lee.
Bounty Hunter - Complete all of Roland's Jobs.
Case Closed - Complete all cases.
Central Scavenger - Unlock every lockbox in Central.
Chief Inspector - Complete 100% of all missions, cases, favors, events, jobs and races.
Detective - Complete 50% of all missions, cases, favors, events, jobs and races.
Environmentalist - Perform 5 unique environmental kills.
Event Driven - Complete half of the open world events.
Event Planner - Complete all of the open world Events.
Fashion Statement - Change all your clothes in your wardrobe or a clothing store.
Fashion Victim - Purchase all clothing.
Foodie - Try 10 different foods or drinks.
Gadgetman - Pick a lock, plant a bug, trace a phone, crack a safe, and take over a spy camera.
Gaining Face - Achieve Face Level 5.
Gold Rush - Achieve 5 Gold Stat Awards.
Golden Touch - Achieve 15 Gold Stat Awards.
Great Face - Achieve Face Level 10.
Gun Nut - Use 10 different firearms to defeat enemies.
Hong Kong Super Hacker - Hack every Security Camera in the game.
In With the Gang - Complete Night Market Chase.
Infowlable - Win 50,000 on a single cockfight.
Karaoke Superstar - Achieving 90% and above for all songs at the Karaoke Bars in HK.
Kleptomaniac - Hijack 5 trucks and collect their cargo.
Man Around Town - Visit Aberdeen, Central, Kennedy Town and North Point.
Martial Law - Defeat all 4 Martial Arts Clubs
Minor Face - Achieve Face Level 2.
Mr. Nice Guy - Complete all Favors.
North Point Scavenger - Unlock every lockbox in North Point.
Officer - Complete 25% of all missions, cases, favors, events, jobs and races.
Pure Gold - Achieve 30 Gold Stat Awards.
Rookie - Complete 10% of all missions, cases, favors, events, jobs and races.
Safe Driver - Cruise for 2 minutes straight without damaging your car.
Sharpshooter - Shoot out a cop's tires while fleeing in a police chase.
Slight Silver - Achieve 5 Silver Stat Awards.
Solid Silver - Achieve 30 Silver Stat Awards.
Spiritual Healing - Pray at all of the Health Shrines.
Strike Gold - Achieve 1 Gold Stat Award.
Stuntman - Successfully perform an action hijack.
Substantial Silver - Achieve 15 Silver Stat Awards.
Super Cop - Unlock ten Cop Upgrades.
Take A Bite Out Of Crime - Complete a Case.
That'll Show 'em - Complete Payback.
Tourist - Win a bet on a cockfight.
Ultimate Fighter - Unlock ten Triad Upgrades.
Wei of the Road - Complete all Street Races.
West End Scavenger - Unlock every lockbox in Kennedy Town and Aberdeen.
Whatever's Handy - Use 10 different melee weapons to defeat enemies.