Prophylaxis Help

This comes with pattern recognition.  You cannot stop something you cannot see, so you must first build up the tactical patterns you recognize by drilling tactics.  Then you will be able to identify moments when you can take the time to prevent an idea from your opponent (or if you even need to).

If you can't figure out what your opponent wants then it's impossible to "see ahead several lines."

It works in OTB. Sometimes kids are coached to get up and walk behind their opponent to look at it from their opponent's perspective.

There are some "prophylactic" moves that are sort of just always around in most positions. The best example of this would be playing h3 or h6 after castling, to avoid any pieces lading on g5/g4 and giving your king some room in case of future back rank problems. Other common ones include kb1/kb8 when you castle queen side kh1/kh8 when you want to push the f pawn, Moving the f knight or c knight backwards to avoid getting hit with a pawn push with tempo ect... You will come to realize that just like every other part of chess, it's all just patterns and you will get a sense of when you need to play these kind of moves.

Yeah, this is a good example.

What you do is you calculate something like Ng5 and, first of all, you check whether you can just ignore it. For example maybe you can just castle, and if they take twice on f7 it's usually a good trade.

But if you can't ignore it, then you find your best defense. Sometimes your best defensive move makes their Ng5 a waste of time. So in that case too you would ignore Ng5.

But after that if you notice you have no comfortable defense to Ng5, THATS when you play a move like h6.

It's important to check like this since otherwise you're wasting time... but all of this is a little advanced since you're probably still blundering simple tactics. In other words even after your opponent plays Ng5 you'll probably miss it can capture on f7, so how the heck are you going to prevent it before it happens, much less know whether the prevention is necessary or a waste of time

Best thing to imagine is "piece restriction" where you can play certain prophylactic moves (usually pawn moves) to restrict the forward movement of an enemy piece. Especially useful against knights. Once you get a strong enough chess imagination to instantly know where an enemy piece can maneuver, these kinds of moves will come natural

Otb you can walk to the other side of the board and look there on your opponents turn (and maybe even your own!) to do the same.

It is good practice to not only ask: "What can I do?" but also "What can my opponnent do?".

It helps to know what your opponent is thinking. If you have time during the game, maybe you can just ask him and then you will know what to play next