how do I get good at bullet?


Speed chess only gives you time to play the ideas and patterns you know very well... the ones in your long term memory.
So to get better at speed chess, you get better at chess in general, which means studying and playing slow games. After acquiring ideas and patterns you'll still need to play speed games to pick up some bullet-specific tricks, but I'd say something like 98% of it is getting good at chess in general, and 2% is speed tricks.
Get a good mouse. You won't want for mouse-slips at the most critical moment.

What llama47 said. Speed chess is based on intuition and understanding that can only be developed by playing longer games.