So I was playing a 1500'ish guy (I'm about a 800-level player) at a 20/10 game and was actually doing pretty good. Ruined the pawn structure and had my rook, queen, and knight deep in his area close to his king and was planing a nice attack on his cornered king which I'm fairly certain would have netted me his rook ... when all of a sudden I move my queen to g3 and his pawn kills it. Mind you, there was no strategy or plan involved in this ... as I'm sure he thought there was since he thought for like 5 minutes before taking it. I resigned right then and there. I simply turned into a sudden and instantanous retard. This was also a long enough of a game that I could think for like 10 seconds or more per move ... I just can not explain my stupidity. So here's the part that kills me: this happens all the time! I know it happens, I know it's a weakness, I try to be careful about it ... but I do this kind of crap ALL the time! WHY!? I know I am capable of the thought process involved in "if I move my queen to the spot diagonally infront of his pawn, he may just kill my queen!"

Experience. Stick your hand in a hot fire enough, and you will learn...

Yea, just play and play, study a few openings and figure out the attacking theme in them! Attacking players rule!

Jeremy Silman recommended asking yourself "What wonderful things does this move do for my position?" before each move. Although he noticed that many of his students never seemed to be able to grasp this concept ("They forgot in the epic heat of battle", as he said.).

Write down your error(s) and keep them near you as a reminder. To err is human.

A lot of elementary blunders can be eliminated by scanning the ranks, files and diagonals after your opponent moves and before you move. This avoids tunnel vision and fixating on one section of the board. It also will help you spot potential disasters before they happen.

Guaranteed to work. If it doesn't I'll double your money back.

But he didn't pay any money in the first place...

Anyways, about the only piece of advice is, before you move, to look for where your opponent's pieces can move to next turn. Look out especially for knights and bishops (rooks are more obvious, an incognito queen is an oxymoron, and a king is pretty obvious himself).

This is a little harder to do in blitz, but like in a lot of things in life, practice makes perfect (and good practice makes perfect even quicker!)