CHESS SKILLS
CALCULATION
The stronger sees ahead more moves and sees around better than the weaker player. KNOWLEDGE The stronger player has more knowledge of specific opening ,middlegame and endgame themes and ideas. 
JUDGEMENTThe strong player is good at assessing the positions at the ends of his branches of analysis. *SKILLS 
INTUITION The strong paer has a well developed sense of determining whether a move looks or feels good or bad. 
*STYLE Different players develop different types of styles. 
ATTACKING Some players enjoy the iniative and attacking the king especially.They are generally happy to sacrifice to maintain the iniative. 
DEFENSIVE Some players enjoy defending and eventually counterattacking. 
SPACE Some players love to gain space while others are happy to play with a cramped position. ETC. *METHODS 
PURDY METHOD The book `Chess made easy'outlines the Purdy method of choosing a move. (1)Do I have a sound combination?If not.. (2)Is my opponent threatening anything?If not.. (3)How how I improve my position?On the opponents time (4)Examine the board for features such as weak pawns, weak squares king safety etc. 
CANDIDATE MOVESThe average middlegame position gives rise to about 40 possible moves.A candidate move is a move that may evnetually be the chosen move. Reducing the number of candidate moves may make the search easier. 
DEPTH SEARCH Depth is the number of moves you see ahead. 
BREADTH SEARCH Breadh is seeing around, and is generally more important than seeing ahead. SUBVARIATIONS ELIMINATION OF BAD
*MISTAKES
Avoiding mistakes is the key to strong chess.
There are all kinds and degrees of mistakes. 
SPOTTING OPPONENTS MISTAKES Recognizing that the opponent has just made a mistake is a useful asset. Experienced players often have a hunch that their opponents last move is a mistake, as soon as it is played. They can then work on this hunch to find a refutation. 
TACTICAL- Tactical mistakes are generally much more serious than strategical mistakes. A tactical mistake will often lead to a loss of material or a mated king. 
OVERSIGHT An oversight is the failure to see a possible move by the opponent. How many chess players have exclaimed "I didn't see that move!" An oversight may be to miss an opponent's threat Even more common, is to allow something that is not even threatened.
STRATEGICAL-There are many kinds of strategical mistakes. 
EXCHANGES, PAWN MOVES It is easier to make a strategical mistake with a pawn move than with a piece move. Every time a pawn advances, it gains space but weakens squares. Pawns cannot move backwards to fill the gaps left behind
POSITIONAL -TEMPO,SPACE,CO-ORDINATION DEGREES OF MISTAKE blunder a very bad move. 

*COMMON MISTAKES TACTICAL MISTAKES Tactical mistakes are much more serious than other kinds. A tactical mistake will usually lead to loss of material or allow a checkmating attack. 

TEMPO WASTING Mistakes which lose 1 or more tempi are very common. Tempo losing moves include unnecesary pawn moves, allowing the opponent to recapture with a developing move and moving a piece more than needed. 
DELAYING CASTLING Many games by simulgivers are won quickly because their opponents have not castled early. 
EXCHANGING WRONG PIECES Don't exchange a well played piece for a poorly placed piece. Good judgement is required to know when an exchange is worthwhile or not. 
WEAKENING PAWN MOVES The weakening effect of any pawn move have to weighed against its advantages. Most players make too many pawn moves. Never move a pawn without a clear reason. UNSOUND ATTACK An attack which was unjustified and is beaten with correct defence often leads to a sucessful counterattack.
 FAULTY COMBINATION/TRAP Sometimes atrap or combination has a flaw in it which the oponent exploits.
 *REASONS FOR MISTAKES LACK OF VISION Inability to see enough moves ahead, or san the board well often leads to a tactical oversight.
 LACK OF PRACTICAL EXPERIENCE Even with a strong understanding, lack of experience may lead to psychological mistakes or other mistakes of a practical nature. e.g. draw
 LACK OF TACTICAL KNOWLEDGE Ignorance of a tactical theme may lead to being caught by that theme. 
LACK OF POSITIONAL KNOWLEDGE Ignorance of positional and strategic ideas may mean that the wrong conclusions may be drawn about a position. 
UNDER DEVELOPED INTUITION Without good intuition, many mistakes are made which a stronger player would have avoided, because the move didn't `feel right'. 
UNDER DEVELOPED JUDGEMENT Without good judgement, many mistakes are made which a stronger player would have avoided, because the move didn't `feel right'. -assessment
 *PSYCHOLOGICAL MISTAKES Overrating your opponent Underrating your opponent Fatigue 
LACK OF CONCENTRATION A lapse in concentration can lead to all levels of positional and more often, tactical mistakes.
 *AVOIDING MISTAKES Avoiding mistakes is the key to success in chess. There are many different tpes of mistakes in chess. 
*PRACTICAL CHESS A good understanding of chess is not sufficient in itself for good results. There are many practical skills which are needed.
 CORRECT SCORING Recording the game should be done quickly and correctly. Making mistakes in scoring, particuarly getting the moves in the wrong column, is very poor and can be a distraction, leading to mistakes in the game.
AVOIDING TIME TROUBLE 

Many players run short of time in tournament games. Play the openings quickly, as his is when a lot of time can be lost trying to make a decision based on incomplete information. When faced with a difficult choice in a complicated position, play the move that is positionally justified. HANDLING TIME TROUBLE One should always keep track of how many moves have been made and not depend on the opponent's scoresheet, which may be wrong. If you do not have time to record the full move, at least tick the move. 
HANDLING OPPONENTS TIME TROUBLE A common mistake is to play very quickly in the opponents time trouble, hoping to prevent the opponent from thinking on your time. This negates the value of having more time and has lost many games. 
TENDENCY TO EXCHANGE It is well known that players in time trouble have a tendency to exchange pieces, as this simplifies their task for them.
 THE BARRAGE Some players like to use this slightly risky method against an opponent in time trouble. The iea is that you plan your moves 2 moves deep. First you play one move, then if your opponent plays the expected reply you quickly whip out your next move. This may be unethical because it often means you will make a move without recording your previous move. 
SEALING Sometimes you have the choice of whether to seal the move or allow the opponent to seal. There is a temptation to seal an unpredictable move to make the opponents adjounament analysis less effective. Many mistakes have been made that way. Sometimes avoiding a committal move like a pawn move or exchange may be ok, provided the committal move is not clearly best. 
ADJOURNAMENT ANALYSIS If you adjourn a game, you are able to use books, computers, your friends, lots of time and you are able to move the pieces around. Adjournment analysis can be good practice for the endgame.
 WAITING FOR MISTAKES Common sense dictates that you cannot hope for an advantage unless your opponent has made a mistake. 
MAINTAINING THE TENSION If the position is approximately even, maintaining the tension can lead to a mistake by the opponent, who may attempt to relieve the ension prematurely.