When assessing the current status in the game, compare the total point value of all the captured pieces on each side. It is quickest to pair like pieces (bishop for bishop) and so forth. Then, the left over pieces will show who has the current disadvantage and by how much.
Understand the individual strengths of each piece and best practices for positioning. Generally, pieces are the strongest in the center of the board where they command the most real estate.
Pawns are strongest together, such as in chains (diagonal lines of pawns). Try not to break this formation unless there is a clear, overriding advantage to be had by doing so.
Knights are weakest near the edge of the board.
The maximum number of spaces a knight can control is eight. If the knight is next to the edge of the board, the number of spaces is cut in half to four. Likewise, if the knight is positioned in the row or column one away from the board edge, the knight's power is reduced to 75% of maximum - it controls six spaces.
You may not miss the power of the knight right away but if you move a knight near the edge of the board, you will often find yourself wasting a move to re-position the knight closer to the action which is usually near the center of the board.
Bishops are strongest on the long diagonals (major diagonals) where they command the most space. It is really not necessary that the bishops be positioned right in the middle of the board where they are absolutely the strongest in terms of the number of spaces controlled.
Realize that the bishop's power can be throttled by the opponent placing a protected piece along a diagonal controlled by your bishop. On the other hand, that piece is pinned in that position if the piece it is protecting is of high value.
Rooks are most powerful on open files. Position rooks on columns that contain none of your pawns. Rooks are also most powerful when controlling the 7th rank for white (2nd rank for black), but only if the opposing King is on its starting rank.
Queens have the most power when commanding the center of the board. On the other hand, they are in the most danger there as well. It is often good strategy to keep the queen one move away from this position and to not shield or block the queen's might excessively with your own pieces.
Kings should always be protected. They are best shielded by lower value pieces.
Aim to control the center of the board.As deduced from the optimal piece positionings detailed above, pieces near the center of the board are at their most powerful. Usually, the game is a fight for control of the center and, when you're in the center, your opponent has far fewer "good" places to choose from. You have power that can expand in either direction -- he'll be relegated to the side, constantly putting him on the defensive.
Pawns can help with this. While your more powerful pieces are attacking, a pawn or two can maintain control in the center. See? They are useful.
Have a strong opening. This will likely determine the rest of the game. A weak opening automatically puts you at a disadvantage for the rest of the game. Here are a few things to keep in mind:
Usually, you'll be best off opening with the d or e pawn (4th or 5th). That opens up the center of the board.
Make only a couple of pawn moves at the start. You want to get your more powerful pieces out as soon as possible.
Get your knights out and then your bishops. Knights range is limited. It often takes several hops to get them into the fray. (Bishops, rooks, and queens can swoop the entire length of the board, whereas the lowly pawn must trudge space by space.) Sometimes, it is less obvious what effect moving a knight might have, so their attack is often stealthiest.
Use all of your pieces. If your rook is sitting back there in the corner, you are wasting powerful ammo. The beauty of chess is that no one piece can win the game -- you need a team of pieces to bombard your opponent's King. So capture each piece- including your opponent's king!
This is especially important if you're playing a skilled player. It's pretty easy to thwart one piece; it's possible to thwart two, but it's incredibly hard to get out of a three-spot.
Never forget to protect your King. Yes, it's important to capture pieces. Yes, it's important to checkmate your opponent's King. But at the end of the day, if your King is unprotected, you'll get checkmated, the game will be over, and that offense you were running will be entirely useless. So while you're strategizing in the front, remember what's going on in the back!
Chess is so fun because you have to think about half a dozen things at once. You have to protect your King while your other pieces are planning two moves in advance. You have to predict where your opponent is going to all the while reading what they're doing now and not letting your own get captured. Once you get the hang of it, you'll be able to do all of these things at once without batting an eye.
Always think a couple of moves ahead. If your opponent made a move, there's a reason why. He's setting something up. He's eying a potential attack. What is he doing? What is he aiming for? Try your best to read this so you can circumnavigate his actions and thwart his plan.
Same goes for you, you know. Maybe you can't capture a pawn on this move, but what move can you make now to set yourself up in your next move, or maybe the move after that? This isn't your normal board game -- every move you make now affects the moves you make in the future.
Never give up pieces needlessly.When your opponent makes a move and doesn't take one of your pieces, take a second to scan the board. Is he in a position to take one of your pieces? If so, don't allow it! Move that piece out of the way or to threaten another piece of your opponent's. Or, what's better, capture that threatening piece yourself! Never just let a piece go.
Unless it's all part of strategy, of course. If you're using a piece as bait to draw your opponent to a specific area of the board, totally let that piece go. As long as you're planning something more devious yourself!