My ELO is 2050. I had not played chess for 4 years until I moved to Amsterdam. In Amsterdam I joined a chess club which has many strong players. Every Tuesday we play 90min + 15sec incremental games each other.(I played 6 games)
I noticed that I could not calculate well enough for the last 3 games which I lost. Also I do not have solid opening knowledge. I started to study tactics from chesstempo. Am I on the right track?
Whenever I haven't played for a while I go through a book with 200 mate in two exercises. Easy stuff, but quite a lot, just to get into gear again. Chesstempo will serve a similar function for you.
But that is just to shake off the rust and not blunder too much. To get back to the playing strength from four years ago or to become even stronger, you should rather train calculation instead of tactics. I.e. not just combinatorial vision but the systematic calculation of long lines. The Dvoretzky books have exercises for that, but those are pretty difficult.
The main point is that in my experience servers on which you solve timed problems aren't really suited to improve calculation. Even just picking random positions from these 10000 puzzles and calculating them like you would in a game is a better way.
You should also reacquaint yourself with your openings, by looking up your old repertoire lines and then play some internet blitz to get a feel for the variations again.
You are in the enviable position of living in Amsterdam so you don't really have to spend money on books yet. The Max Euwe Centrum has a library of chess books in many languages, entry is free and you'll find the newest books on every possible opening and avenue of chess improvement.
There are numerous books that might help you but the best way to get better is to practice, practice, practice. Play as much as you can and try to keep track of the moves in games which you play so you can go back and review what you did wrong if you won a game or what you did right if you won.
I would recommend the book by Polgar "5334 Problems, Combinations and Games." It is good way to get into the habit of calculation.
I recommend studying openings with a computer. This will help you identify why many moves are bad, something opening books don't tell you. It is a lot more important to know why a move in the opening is bad, than why a move is good.
For players of all levels, including masters, it is often a good idea to study the endgame because usually that part of their skill is the weakest, so you stand to get the most by studying it. In other words, it is low-hanging fruit.
I would recommend Nunn's books, especially "Secrets of Rook Endings".
Also, "Secrets of Pawn Endings" by Karsten Muller.
Learn just those two books solid and you will be amazed how you can beat the crap out of anybody in an endgame.
One final comment about the endgame: often in modern swisses with short time limits you have to play the endgame really fast, somethings blitz sudden death. In those situations the guy who knows the endgame ahead of time will CRUSH the other guy. Even with time on the clock it can be really hard to find the right move in an endgame. You have to know it ahead of time. In a blitz situation, people will play just incredibly bad moves one after the other in an endgame.
