Here are great strategies for Dots iOS and Android game.
There are three types of moves: squares, making a square in one move, and wasted moves. Don’t waste moves.
If you haven’t traced a square in first two seconds of the game, on first or second move, restart.
When making a square, eliminate longest possible chain if the color you are eliminating is scarce and shortest possible when it is abundant. When the chain is three long, and removing third dot doesn’t affect square creation, always remove the third point.
Try to stay close to the bottom.
Use the first useful move you notice.
When there is a square, use it.
Use a shrinker whenever you notice how to make a square with one shrinker.
Extend time when you are in a good square run.
Expanders are not that great, given the price. They do allow to continue square runs when there are no useful moves. If you use expanders, you will probably get higher scores, but will likely need to buy dots.
When multiple squares exist, use lower ones and ones with more abundant color first.
Doing square runs fast (really fast) is more important than choosing the right squares, when there is choice.
Restart when you can’t find a useful move in a couple of seconds.
Turn off sound in settings. This way, the phone doesn’t buzz.
And finally don’t check time or score.