Save your coins for the end of a round. If you only need a few more moves to complete a level, you can spend 70 coins to get three more moves. Use these tactics on tougher levels that do not include a lot of spare moves.
Removing dark jelly
If you are having problems removing dark jelly, make a couple quick three piece connection to shift the jelly. Try connecting jellies that are a color that is rare on the current level. If you save one color, you will still have a chance of making a super jelly. You may then have the pieces required to get rid of the dark jelly.
Complete small combos and save one color of jellies to create a super jelly combo. The last jelly you connect is where the row or column will be destroyed. Try to set things up so that the last jelly in the combo is in the row or column you want removed.