Thanks guys. Most common tip is to play 30s (why not 45s first?). Other tips: - time is more important, not position - learn how to play quick openings - play safe pre-moves, move quick but without dropping all of your pieces
Some, like @Rrhyddhad , think learning better chess skills is important, some seem to deny such importance. It probably depends on how fast can you apply your knowledge, thus learned openings, strategies or tactics are only useful if they can be applied through premoves. That will depend on your ability to consolidate knowledge to apply them quickly (automatically).
I'm quite sure that people who reach 2000 easily (or even 2400) are born with different brains, brains for chess. Brains which can memorize and apply patterns very quickly. Only in correspondence chess that this is not an important skill. There I can stay above 2300 easily and my next goal will be 2500.
@EvilChess add one important one: Get your king save as quick as possible so you're not wasting time defending it from all kind of checks, and other attacks.
Initiative is more worth than a pawn, in Bullet. What I do, with white, is sacrifice a pawn in the opening, to get the initiative. I play e4 and d4 on premove, and when my oppponent captures one of my centre pawns I play c3 or f3 to sac a pawn which I can take back with my Knight. I make 3 premoves, in the first 4 moves. Which helps me, on the clock. And when it comes to an opening, with black I play the Lion variant of the Philidor opening. An opening that looks calm, but is not. I like it. Just because I can fire out like the first 10/15 moves without thinking. d6 - Nf6 - Nd7 -e5 -c6 - Qc7 - Be7, h6, g5 and Rg8 (then is bring my knight from f8 to g6 to f4). At this point I usually used like 1,5 sec, and my opponent like 8 or 9 sec. Giving me a comfortable a head start.
Yes, learn a simple opening which first moves you can play (almost) without thinking. That helps. And, of course, solve puzzels so you recognise returning certrain paterns quicker.
I always would like to write a book about bullet chess, like a strategy book. Because for example, in certain positions, especially in mutual time trouble, it's a better choice to not make (or search for) the BEST move but rather for the most aggressive move. From the heart, instead of the head. That's a funny paradox with regular chess.
Oh, and the last tip. Play, play and then play some more.