In my opinion this is the most important part of controlling and winning squash..It sounds so easy..stay near and control the 'T'. If you can do this you will likely be successful.
How do top players make it look so easy? But when they play someone just a little better everything changes..clearly the pace of play, quality of shots (especially length), volleying ability, anticipation and you need to be pretty fit to maintain it for a full match. There is a lot that goes into controlling the middle part of the court.
It can be difficult to get an opponent who volleys well off the 'T' and difficult to stay near it against someone who hits the ball hard or has tight length. But the real question we all want to know is how can we improve our ability to control the 'T'? It can help a lot by just watching yourself play on video. How often did you let balls go to the back that you could have volleyed? You don't need to attack the ball just because you are volleying it. A lot of players also have trouble timing a volley meaning that they tend to avoid trying to play the shot altogether. But nobody gets better by not trying. So my first bit of advice would be to not worry about the result of the volley, just that you are volleying.
It takes a lot of practice to play a delicate volley drop shot. Make sure your racquet is prepared early and keep going got them. If you lose confidence in the drop you can always try a volley boast. If you aren't going short on the volley then your opponent will not feel worried when you volley the ball right back to them or cross-court.
Outside of games, focus on volleying everything when you're doing drills and practice your volleys with a ball machine or while solo hitting.
Not only does controlling the 'T' mean less running for you, but it takes time away from your opponent. Keep fine tuning these shots and one day you will notice that you rarely visit a back corner..until you play a stronger player..and then try to figure out how they're doing this better than you.