Endurance - recommend runs 30min Max; build up to doing this till it is comfortable. If you cannot run, and some people are not natural runners, then cycling may be more user friendly, once again work off your heart rate. Sessions of swimming will increase oxygen uptake if your wind is a specific weakness. 400m runs, this specific exercise will give great endurance. Start with 1x 400 and build up to doing a number continuously. Always be mindful not to train excessively.
Recovery - Squash encompasses quick recovery so sessions of sprinting and recovery (fartlek type training) should be incorporated, but as before monitor your heart rate. This can also be done on a bicycle as well.
Ghosting - By using ghosting drills similar to 120's; Dog and Bone etc you can incorporate endurance and correct movement in the same exercise. Increase the exercise time and lessen the recovery similar to interval type training.
Strength - This component is required to give continuous effort; lunges can build the power required for continual reaching and recovery to the T without fatigue that will have you hanging at the back of the court during the fifth game.
Flexibility - Ensure to incorporate sessions of Yoga, Martial Arts, Pilates, Boxing etc to ensure suppleness and core strength.
Continual hitting - incorporate single practice sessions of consecutive drives with power to build endurance of arm back and shoulder muscles and increase accuracy with your shots with power.
Do not exceeding your max heart rate as this will not give you any greater benefits (220 - your age) Have adequate rest sessions between training sessions to give your body time to rebuild.
With the coach involved, train to make your weaknesses into strengths; this will ensure your improvement. Look at the resources you will require to reach ultimately where you wish to be. (Technical; Tactical; Physical; Mental) Your training must encompass all these areas or you will not succeed.
The best way to improve anything swing related is repetition; however it should be noted that you should also look at what you are doing to ensure the correct technique is practiced. This will ensure a swing that will repeat giving consistency and inbuilt deception by making all shots look the same, the right swing technique is very important.
The Knock-up during the warm-up session before the match should not be wasted, this is a good opportunity to feel the court and try and to find the right length, if you get the length right everything else will drop into place.