I had a look at your last completed game to get an idea of where you are at. Before I make some suggestions on books, I wanted to discuss a couple positions.
ok, first position.
You are Black. White has broken the basic rule of developing minor pieces and playing to control the center and instead is taking a cheap, tactical shot at you. While Nf6 is a good developing move and you attack the Queen with tempo, you miss that the Queen has a good square to go. (e5)
Next time consider Nc6 instead, developing a piece and defending your e pawn.
Black has managed to escape real damage and stands better now. How do we know this? Let's consider
1) White is up a pawn.
2) Black has a two developed knights and a centralized Queen and a move.
3) White's pinned knight is gumming up the natural development of the Kingside this should be like a red beeping light. If your opponent cannot get easily to safety, then you should focus less on recapturing your pawn and more on how you can crack open the defense and get at him.
So what are some reasonable ideas here
1) Qxc2 - sure, ok you get your pawn back not a horrific decision but not terribly enterprising either- you don't get to keep your left over pieces at the end of the game after all.
2) If white were to move, they would play either d3 opening a diagonal with tempo, or just Qe3 blunting your Queen's pin and simplifying things So this calls for something more active from Black something like Nd4. First it prevents Qe3 as the Knight check on c2 forks the Queen. Second it is going to capture that c pawn with check preventing White from castling. Note that if White tries to stop the threat on c2 with Na3 then Black can just chop off the Knight with the dark square Bishop. So given the choice I think I would opt for Nd4 and the attack.
Ok, here what is called for is a little danger sense. Whenever your queen goes on a sortie into the enemy lines, it is very important to be able to get her back out alive. This means keeping track of escape squares- here after the move Nf4 your danger sense should be going off. Your queen has only one way to escape and it is being threatened by the now freed Bishop.
In correspondence chess, where you have ample time to decide on a move, it can be very helpful to keep a running list of aspects of the position your looking at- sort of like a checklist of dangers etc and when you are deciding on a move, you make sure it doesn't violate anything on your list. Chess is a visual game, so that means really looking and moving the pieces around until you see them naturally.
In time, you will be able to juggle priorities without any conscious list, but it is critical to develop this ability if you want to improve as a player.
Now, as for a chess book.
I think you should have one book like "Logical Chess move by move." Something that annotates every move so you can really understand the thought process with each move.
As a second book, I might actually suggest something out of GP's library and that would be "the quickest chess victories of all time" - and this is an odd choice I admit. My thinking is the games are short, they all are horrific car wrecks of games where one of the two sides violated opening principles and were punished tactically for it. This is not a book to study traps, but to play quickly through the games so you can see classic motifs etc. and develop your intuition. If you play through all 2000 games I am sure you will benefit tactically and you will see how breaking the "rules" of how to open a chess game get punished.