Hello @Dodotron
The most important thing in PvP is for sure the knowledge about the current advantage/disadvantage status ingame.
Replays/Theory is very usefull, but only a little thing to get a better knowledge. Its better to analyse your own replays to figure out your own problems & mistakes.
You've to trade units efficiently & to do the correct "move" ins the current situation. Thats the key about the game history.
PvP is mostly learning by doing. You'll get a feeling for the current game situation if you played enough matches.
After this, you know directly