Every turn you should review all the pieces on the board that can be taken and aren't guarded, for both black and white.
After that's done you should count the attackers and defenders of a square (possibly occupied by a piece) to determine if you control the square, or can capture on it. You need at least as many defenders as attackers to defend a square. You need one more attacker than there are defenders to attack it. (counting pieces is easier than calculating the actual captures)
next you should look for tactical moves.. You can only learn to see them by getting a book on tactics and practicing them every day. You need to burn it into your head as this is extremely important.
before you finally make your move take a second to make a sanity check and make sure you didn't miss everything, quickly check over the above steps. Make sure you're not ignoring an attacked piece that isn't defended, or hanging a piece when you move (by moving or blocking its defender)
That's a good start. Do those things every turn.
Here are 3 lists I have gathered that really help with *basic* thinking about your chess moves.
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THE ANALYTICAL METHOD OF CHESS THINKING - Lev Alburt
The analytical method provides a 'reality check' as you contemplate your next move. You put yourself in a critical mindset, analyzing your opponent's move and your intended response against a checklist of simple questions designed to prevent you from making obvious errors. Before each move, ask yourself:
Does my opponent's last move contain a threat? If so, deal with it.
Are my own pieces all adequately protected? Has my opponent left a piece exposed to capture for free?
Is my King still safe? Is the opponent's King vulnerable? For example, is it possible to sacrifice a pawn to prevent the enemy king from castling?
Did my opponent meet the threat offered by my last move? What does my opponent's last move now allow me to do?
Do I still have pieces that need development? Can I move a Rook to an open file? The d or e-file? Is it possible to double Rooks or a Queen and a Rook on a useful open file?
Does my opponent have a weakness that can be exploited? If so, how can the weakness be exploited? (Find a way to exploit a weakness that involves making a plan!)
Does the move I plan to make overlook something very, very simple, such as the loss of a piece or checkmate? Train yourself to look around at the position "with the eyes of a beginner".
The analytical method isn't just for the middlegame. Use it to validate your opening and endgame play as well.
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SIMPLE STRATEGIES TO ENHANCE TACTICS - Michael de la Maza
Improve the mobility of the pieces.
Prevent the opponent from castling.
Trade off pawns.
Keep the queen on the board.
Pick a weak pawn/square and attack it.
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ATTACKING WEAK PAWNS/SQUARES - Anonymous
Step #1: Identify the weakness
The five steps outlined here are relatively simple but they account for many victories and they are present in one form or another in most master games. The first step is simple enough. You will win many games if you train yourself to be aware of and to identify quickly all of your opponent's pawn weaknesses.
Step #2: Fix the weakness
Prevent the pawn from advancing by either blockading it (filling the 'hole' with a protected piece) or by controlling the weak square in front of it.
Step #3: Attack the weakness with your pieces
Once you have identified and fixed the weakness, it is time to attack the weakness with your pieces, but not your pawns.
Step #4: Your opponent will be forced to defend the weakness with his pieces. If you have successfully carried out the first three three steps, your opponent will have to carry out the fourth step. For every attack upon the weak pawn, your opponent will have to find a defender.
Step #5: Then, AND ONLY THEN, attack the weakness with a pawn.
By the time you've completed step #4, your opponent will know that there's trouble ahead. All of your pieces will be active, focusing their energy upon a single fixed point. By contrast, all of your opponent's pieces will be relative weak, defending rather than attacking a weakness. The final step is simple enough. Attack the weakness with a pawn.