What is some basic advice for playing blitz or rapid? A decade back i used to play chess, but just OTB and without time control. I now got back into chess and often play something like 15+10, where I very rarely lose on time and I am now rated ~1500 on Lichess. I tried playing shorter time controls but i lose almost every game (rated 900 blitz) on time. I also dont seem to improve at all an do not really know where to start to get better at those time controls. Are there some ressources that could help me improve or should i just change my playstyle for blitz?
Welcome to Chess StackExchange!
You say the transition from games at 15+10 to blitz sees you going from rarely losing on time to almost always losing on time.
Can I ask if the blitz is still with increment eg like 5+5 or some such?
When I switch from say bullet to 5+5 to 8+5 and such it always takes me several games to get into the rhythm of the new time control.
Do you have a sense at the shorter time controls that you are falling behind in the opening phase, middle game or end game?
Are you spending too much time in the openings to get a good position but then run out of time to win?
One way to cope with the time issue is to play a small number of quieter openings. You will learn how to play their characteristic pawn structures and where to put your pieces.
For example I aim to play as white the London System and as black against e4 the French Defense.
Against d4 I like the NimzoIndian.
There are online games repositories with notes that can help you.
A good area to study is the endgame, an extra effort here will dramatically improve your results.
Rook and pawn endings are quite common and it's worth studying them. I find it's the area where my opponents often stumble.
Always try to get your rook active even at the cost of a pawn and remember that whether in attack or defence the rook belongs behind the passed pawn!
Pay particular attention to your king safety or your opponents lack thereof.
In a time scramble an exposed king position can be a nightmare.
Best of luck!