How to beat experts
So it will probably be misleading if I don't talk about beating experts in different time controls so first of all the key to beating an expert are TACTICS! You probably have heard about them a lot but one can never study enough tactics. I know of someone who was very talented but did not have the time to play chess and completely stopped playing competitively for 4 years. Now after the first 3 year hiatus he tried playing some games and he was originally 1500-1600 strength (only rated 1300) strength and when he came back he was probably only 900. Within that last year he did many tactics and is probably 1600-1800 (rated 1400 because he hasn't played in enough tournaments but he won his last two with 5/5 and 6/7.) Now in a slow time frame against an expert, take time so that you don't drop any pieces or make positionally worse moves so that your opponent does not have more active pieces. Also an idea is to trade everything off quickly but that will require you to be really good in endgames if you want to win. In fast games take enough time to not make mistakes but make your moves on par or faster than your opponent. If you are a true chess player you should be able to read ahead so when your opponent is thinking, start thinking about good moves that he can play and think of counter moves to speed up your move time. Fast games tend to lead to mistakes, but if you can just take a second to run through it before you move, you can avoid mistakes. Even if you make mistakes, you can still win on time however. Here is one game that I played against an expert.
So in a long game (90 min+ 30 sec inc or longer) then take as much time so that you can prevent any mistakes. But there is also a flaw in that: If you stay too long at the board you will lose concentration, so stand up walk around and look at different games so that when you go back to your game your brain will be refreshed. If it is a blitz game, just don't make any tactical mistakes and move faster. If it is a bullet game then make it hard on your opponent and move faster than them (it won't matter if they lose on time, but don't lose before their time runs out either). No matter what, keep it simple. You are probably not going to win against an expert playing some obsolete opening unless you are of similar strength. Please share your games of beating experts if you are not an expert or almost an expert :)