Squash is an art, a science and a physical test. For those players who have absolutely fantastic natural skills and powers, the game is simple: hit winners. For the other 99.9% of us, our mental computer needs to continuously employ the risk/reward formula - that endless multitude of considerations that determine which shot to play:
What options do I have? Is there a definite correct shot to play now, even though it is obvious? What shot did I play last time I was in this position? What shot am I being (even slightly) forced to play? What options can I show I have?
How tired am I? Will the attempted shot I play from here be worth it? If I miss it, will it put me in a much worse position than the position I am in now? Even if I miss the shot - but I don't miss it by much - will it be worth it since I will anyway force a loose reply and I will have created doubt for the next time I am in this position? Overall, have I been too positive or too negative so far? Is this the right shot to really delay and deceive or is it too tight or too obvious a shot so that the benefit - although there would be some - would be more if I waited for a slightly different ball?
The computer may work out the risk/reward formula and simply conclude "play straight drive deep". Indeed, it will rightly conclude this often. Risks and rewards of a multitude of shots will be calculated continuously and shots selected accordingly.
The tighter the ball to be played, the straighter will be the selection. The looser the ball to be played, the more variety is available. A continuous correct selection of shots quickly becomes a virtuous circle where the rally will inevitably end with your winning shot. A continuous incorrect selection of shots quickly becomes a vicious circle where the rally will inevitably end with your losing shot. It really is possible - unless the ball is very tight - to go "forward" in the rally every time you play the ball. In other words, having played the ball, you should always be in a better position than you were just before you played it. When coaching, my most commonly used word is "nothing": when the pupil hits a shot that achieves nothing - normally an "attacking" boast that actually comes back to the middle or a cross-court hit wide and/or too obviously. In fact, they are less than "nothing" shots: the player is in a worse position than they were just before they hit it.
If you can't or won't do any of the above, you had better start some serious training. Good players do not waste a single shot - the energy clock is ticking.
And my final words of advice is "Remember that a TITAN racket will always help ......"