Pre shot
The other posts have great advice here.
Others have posted their steps so I will not duplicate that.
The pre shot routine is the foundation from where you will make every shot and get postion to your next.
It is like building a house, you don't start with roof, you create a rock soild foundation that everyhing else will build on.
Instruction will be the best way to find out where your errors are. I wish I would have gotten some earlier on. I still have bad habits that I am trying to break.
A fast tempo can be just fine, just make sure you do it the same way every time.
Now stick with your routine!!
Here is what I have done to help my game.
Then the next time you miss a shot or make an error you can then make a mental note or actual one on what you did wrong. Most of the time it will be something in the pre shot routine. If it is a hard shot and you missed, well you are not the first person to do that.
Let's call it self diagnosis. This is how we as playes advance.
From there you can add or subtract from your routine and then make the needed adjustments.
On the mental side of things I try my hardest not to think about what will happen if I make a shot or miss a shot. I really just try to focus on makeing the ball and getting my next postion. This is easier said than done but I am getting better at it

Now if you don't know what you are doing wrong, then you need instruction.
Best of luck and keep playing.