The little things

Any chess player will know the agonizing feeling of coming very close to victory and then have that feeling evaporate as the opponent suddenly bounces back because of a weakness that he/she exploited. The agony is due to the fact that this weakness (maybe plural?) was one that the player chose to ignore early on the game as it would not be a potent threat later on, and that the player would 'deal with it' later. However, it turns out to be the only thing wrong in an otherwise flawless position. It could be anything from an isolated pawn to a 'holey' pawn structure, or even an unsupported piece which was hidden from sight but exposed after a tactical melee. A standing principle among chess players should be to make your position ironclad and then attack so that the force of a counterattack is reduced. These are some of the common factors overlooked by some players:

• The useless piece. In many games, we have that one poor piece that simply cannot break out of its own camp and participate, so the player leaves it, hoping a raid can be conducted with the remaining pieces. It's important to remember, you need each and every piece to be involved in an attack. If there's a piece left behind, make sure it's doing something useful like defending multiple pawns or protecting the king. A bishop on f1/f8 is an example of this. If the piece is trapped by its own men then it can become a liability and an annoyance. A classic example is black's dark square bishop in queen's gambit game or even white's light squared bishop in the Ruy Lopez (it gets freed up if the center isn't cluttered). It seems like the bishop is protecting its pawns and so everything is alright, but its value as a piece would be greatly increased if it could breathe. Launch an attack, and the opponent won't have time to target pawns.
• Icky pawn structure. Pawns are indicators of territory. Pawns should be arranged and advanced so as to cover as many squares as possible. Putting pawns on the same squares as each other is bad as the zig zag formation leads to the genesis of 'holes' which are outposts for enemy pieces like knights.

Here, black has a terrible weakness on g6. Furthermore, the pawn on g7 is backward. A weakness so close to the king is dangerous and should be tended to immediately. Doubled and isolated pawns are obvious weaknesses as not only are they vulnerable, but you've lost your ability to create an additional passed pawn as one pawn is hindering the advance of the other/others. These should be advanced and/or exchanged off or even sacrificed to create imbalances.
White has a disastrous position here. The pawns are hanging on for dear life and the bishop is unable to help much. Black will occupy f5 and maybe e4 and force white into a zugzwang.

• Stifled king: It's hard to keep under control in every game, but keep your king out of danger until the endgame. Make sure your monarch has escape squares and a little wiggle room for random checks and tactics. Many a time, the position is close to equal, but a back rank tactic (for example) can lead to loss of material. You need either a rook to control the back rank or a piece to block a check. Try to keep the king submerged in the early stages of the games and let it surface when things have calmed down.

For example, here white wins a piece after rook takes bishop on b7. If black recaptures then Qe8+ leads to mate in 2 moves. Having said all this, it's also important to make sure the king stays active and is not left far behind in the endgame. Again, in an equal position, the opponent's king may be able to gain some ground and put pressure on pawns, etc in the endgame. As major pieces get exchanged, move your king to the center slowly.

• No room: This is a follow-up to the useless piece point. Even if a piece is in a useful position, it may be unable to spread its wings, which is heartbreaking, as it probably had some real potential. A rook on the 3rd/4th rank, for example, which has been brought out too early may be prone to a knight fork. A queen brought out to a5 (edge of the board) often gets snapped up in Sicilian games as the player becomes too greedy (the Poisoned Pawn variation). It pays to be vigilant and on the lookout for traps.
• Undefended pieces: Some pieces down the board (away from home base) tend to be neglected until the end of the game. They're on seemingly innocent squares but can be often be snapped up in tactical combinations. 

Here, the winning combination is 1. Bh7+!, snapping up the rook after the queen check.

Be careful of the little things. In the end, they may even be the difference between a draw and a win.