Paying attention to one aspect of chess can improve the performance of nearly every chess player. That factor is prophylaxis, ie actively thinking on behalf of the opponent and thwarting their initiatives. Reading this you probably say, "Sure, what else is new?" Me too. I've lost count of the number of times I told myself to think actively for the other side. Yet I still fail to do so. Given that I put a fair bit of effort into chess and that I want to improve, it's worth asking why I don't practise prophylaxis more than I do.
I have an emotional resistance to putting myself into the place of my opponent. Instead, I want to see the game from my perspective, to focus on what I want to do, not on what they want. I don't like to think about how the opponent can hurt my position. In other words, the problem is an emotional one. Prophylaxis is not enjoyable and we want to enjoy playing chess. Prophylaxis requires us to apply emotional intelligence to chess, rather than following the dictates of the ego.
The most obvious failure of prophylaxis is missing the opponent's response move, especially a check or capture. Yet prophylaxis goes well beyond the basic skill of analysis, ie "If she does this then I'll do that." It has two parts. The first is creating tactics and game plans on behalf of your opponent, exactly as if you were playing for the other side. The second is thinking up counter-measures to frustrate these ideas. Compared to a player who only thinks about their own plans and how the opponent can react to them, the player who practises prophylaxis puts in twice the work.
Never assume that the opponent makes a move without a good reason. Of course, their move may be useless or even a mistake, but make sure you analyse why they made it. Paradoxically, I both over-estimate my opponent's possibilities to launch an attack as well as spending too little time on working out those possibilities. It's really a form of denial and it eats away at me. So I want to get out of the fear of exploring the opponent's attacking possibilities. Something makes me hurry and miss moves for my opponent, especially aggressive ones. I need to think of their most aggressive move at every turn.
Even when I expend a lot of energy to calculate a line, I still miss moves for my opponent. Why is this so? Playing like this amounts to playing a game of chance, that the move my opponent chooses is not worse for me than what I thought was his optimal move. Too often, their move is stronger than the one I thought of. The good news is that I can look forward to a major improvement if I find a way to largely eliminate this great weakness in my game.
Here is my remedial strategy. On every move write down my next move and what I think are my opponent's best strategy and tactics. Think what is their most active move and the line it initiates. Allocate not 50% but 60% of my effort to finding their best move. If my next move does not look good after this analysis then repeat the process till it does.
Prophylaxis is not an add-on or a kind of insurance, but goes to the heart of what chess is about: a contest between two people, each of whom hopes their ideas will prevail over those of the opponent. It may seem less fun to apply prophylaxis, but then, winning is more enjoyable than losing.