defense against kingside attacks

Most of my recent losses have resulted from making mistakes when my opponent launched a kingside attack. I posted an example below. I can find the mistakes when I review the games, but I'm hoping for some tips and general principles to avoid the mistakes in the first place. (I'm sure people can find many weaknesses, but the kingside attacks seem like the most glaring problem now.)

Thanks to both of you for the very detailed and helpful comments. I'll go through them more carefully. Certainly, there are many weaknesses in my play, but handling kingside attacks is the most glaring one right now. That game wasn't a typical example of my problem, since my position was so bad even before the kingside attack. (I usually respond to d4 with d5, but I tried something different in that game, obviously without much success.) Also, I didn't see Bxh7+ coming. Here's a game where I think I was in good shape, saw the kingside attack coming, and then collapsed anyway:

I'd welcome comments on this particular game, but I'm also interested in generalities.

To respond to your specific questions, paulgottleib, I didn't see the bishop sacrifice coming. I don't remember my thought process, but when I was considering my opponent's counterplay, I probably neglected to think much about Bxh7 because my king was guarding that square. I also didn't see the recapture and mate on the open file. That's the sort of obvious mistake that I seem to make more often against kingside attacks than I do in other positions.

Whenever you say to yourself "he can't take here because that is guarded," you have stopped looking too soon. Go through the sequence in your head anyway. The same is true when capturing one of your opponent's pieces.

In my experience of low level games , when you lose e5 square to an enemies pawn, you need more pieces (Bg7 Nh7 Nf8 etc) on the kingside to prevent strong (usually gambit) attack to your king.

Thanks again for all of the comments--especially the general points about keeping the initiative and about permanent liabilities. I understand (at least to some extent) the concept of the initiative, but I think that I underestimate its importance when my king is under attack so that I settle for purely passive moves. Among the many errors that pfren noted, rushing to capture the queenside pawn is a typical type of error for me. (Fortunately, I don't as often make such blatantly obvious, cringe-inducing tactical blunders like overlooking the threat of Nc7+ and giving away the exchange.)