what improved your bullet rating?
a better mouse and internet
I'm >2000 on lichess bullet, does that count?
First thing you have to get down is continuously checking the clocks no matter how chaotic the board is. You just can't get very far if you are tunneled on the board. Knowing when you have time to calculate and when you don't is too useful to not have.
Having openings that you know really deeply is super useful. Being able to be blitz out the first 10-15 moves quickly saves you a lot of clock. In the french exchange I'm often at move 15 with 55 seconds to their 40 seconds.
End game knowledge is also useful. While a lot of bullet games don't reach the end game, when it does being able to convert quickly and find unintuitive moves makes the difference.
An underrated aspect is knowing when to slow down. Often good to take 5 full seconds to understand the position, find a complicated line, and calculate it you can then blitz out the moves rapid fire.
But most important by far is consistency. It's not finding crazy tactics, it's going 60 moves in 60 seconds without hanging a piece even once, and not missing your opponent hanging a piece even once. Most bullet players fall apart late into the game, if you stay persistently consistent you can overcome massive material and time deficits.
