Its an interesting topic, and requires some tricky answers… but trying to keep it simple:

1. movement around the court is most important to increase your level. The big difference between standards will be the speed and quality of movement around the court.
2. shot quality (includes consistency and technique). If you can make fewer mistakes, or maintain a higher shot quality than before (i.e. a badly executed shot is the same as a mistake e.g. short lift), then that will massively improve your game. This is tied to stamina, tehcnique AND mental fortitude – as you get tired, your shots get worse – you need to make no mistakes even when very very tired. This is a mental struggle, and its a tough one!
3. shot selection – tactics will keep you in the game. If you can move well, keep getting to the shot, keep playing high quality shots AND choosing the best shots for the situation, then you will be playing very well, but quality of shot is more important than the selection.

Then you get onto the other stuff e.g. physical fitness (being able to go at your fastest for longer, increased physical power etc), positional awareness etc.

My theory is that, once you can move fast and have good consistency, you then have the foundation to build the remainder of your game e.g. start making smarter choices etc etc. But if you can’t get to the shuttle (1) and can’t consistently hit a reasonable quality shot (2), you do not have the skills required to stay in the rally!

Good topic!

Matt