The development of leg and arm strength involves two steps.
1-Increasing the strength of the muscles that are used during the squash game
2-Increase overall muscle speed and endurance

Breathing and mental concentration at all times is very important. Always exhale on exertion and as you inhale imagine you are bringing in energy.

The first step can be achieved by using conventional weight training programs. For squash, the strength training relates strictly to the upper body since leg power is developed in the anaerobic on court program.

Players should start any strength workout with the flexibility warm-up. Using light weights such as dumbbells or ideally pulley weights, you should do 3 set of weights (20 times, 10 times and 5 times) increasing the weight after every set. The 20-10-5 routine will build up strength and local muscle endurance with little bulk. For each set use a weight which makes the last few repetitions difficult.

The second step involves introduction of specific drills to allow the player's strengthened muscles to do fundamental squash movements at progressively higher

Weight routines         Target muscle groups
Chest/ bench press   - Pectorals, triceps, deltoids
Hamstring curl           - Hamstrings
Half squat / leg press - Quads, gluts, hamstrings, spinal erectors,
                                 deltoids, abdominals
Bicep curl                 - Biceps, brachialis
Lateral pulldown        - Lats, biceps, traps, rhomboids, deltoids
Calf raise                  - Soleus, gastrocs
Tricep press              - Triceps, lats, pectorals

Motivation

Remind yourself why you play: To have fun, to improve and progress and to be with others who enjoy the game

Analyse your mental strengths and the areas in which you would like to improve. Approach each practice and match as an opportunity to learn

Effort is the key to learning and improving. Evaluate your level of effort and constantly seek to raise to a level of effort

Develop goals that you work on daily. Process goals have to do with HOW you play, rather than the result or outcome. Emphasising the process will lead to the strongest performance. The strongest performance will produce the highest possible results.

Learn very simple relaxation exercises to help you calm yourself when you need to before or during your match. Such as :
=Taking a series of regular deep breaths and slow exhaling
=Having a word or phrase that you associate with feelings of calmness and relaxation
=Alternating squeezing and relaxing your hand as it grips the racquet
=Focusing your eyes on the centre point of the strings of your racquet

Think of concentration as a skill. It is closely connected with the abiltity to stay relaxed in competition

Analyse what you say to yourself as you play. Identify the things that you think or say to yourself that are not helpful and replace them with words or phrases that are positive, encouraging and conductive to strong play. Analyse your posture, physical appearance, and expression when you play. Adopt and practice a look of confidence, strength, energy and toughness.

Develop a plan that helps you prepare mentally and emotionally to play. Analyse its effectiveness each time you play and refine it periodically. Identify moments of challenge or potential distraction that may occur during your matches. Plan your ideal response to these challenges and practice them daily to prepare for match play

Approach competition as an opportunity to measure your play and progress against your own standards. Keep a performance journal, analysis of the mental and emotional aspects of your play.

Links to other sites:
Should kids do weight training? Prevent sports related injury