By now using black holes to suck up enemies may not be a good idea because they will fill up too quickly. Try not to shoot them unless you know you can destroy them as soon as possible. A technique you should start getting good with is making circles around the play area, shooting in front of you as you go. This will allow you to shoot a path for you to keep moving through. Enemies will start to gather behind you as you do this so whatever you do DONT double back and go the opposite way unless its clear and you absolutely must. You should also try not to stay in one place, you will get swarmed faster than you expect.