You cannot improve in all of them in the same time (even if playing a lot of matches will make you understand what to work on).
The best thing in order to get good in this game is to (obviously) play a lot, having a coach that gives you ''homework'' and doing them, and if you improve that greatly not only making the homeworks but creating a new series of exercises all by yourself that gives you the chance to improve.
So how do you get the ability to make your own exercises?
first you have to understand the game at a deep level. Here are the basics:
1)throw the ball at the side (preferably in the corners);
2)you must stay in the center.
Just by knowing these 2 simple concept you can create a lot of exercise in order to improve your game.
You can focus on moving in the best way (not how you think)
or you can think about improving your shot maybe starting by increasing the angle of your plate and by preparing the shot (opening as i say) before.
In order to get a deeper comprehension of the game you need to develop 3 kind of knowledge:
-Intellectual -Visual -Physical
1) learning about the game, rules, know-how, tactics and info
2)watching squash matches both online and live so that you get to understand movements, tactics, emotions(they play a huge role in the decision making processes) and techinique.
3) Doing exercise/training/ matches so that you internalize (slowly and constanly) all the concept that you need to understand.
It Takes years to become good at something, same is for squash. if you accept this the fun will start soon!
Tips to train alone
Practice alone is very important also because you get to have the control over everything you do.
The hardest thing is to accept that it has to be done.
It can be boring or even feel awkward (i honestly was ashamed of running in public) you just have to practice the thing on ''your level'' and keep on trying to take them over the edge.
Dont waste your time trying the impossible shot if you can't even make a straight shot.
Just do what you can and try to improve both in a quantitative way (i.e. number and speed of shots) and in a qualitative way (i.e. quality/precision).
Time for practice is the most valuble thing. Even a afternoon of just having the raquest in your hands is better than none!