Wait, did I already shoot that target? Where am I going, what am I doing?!
Memory Stages. What tricks do you use to help you remember your stage plan?
In USPSA, you can walk around outside the fault lines and count targets. Get a round count from outside the fault lines, then count again from within the fault lines. If the numbers don't match, you have a problem.
If there is a particular target that you can't figure out where it's available from, stand in front of it and look back at the fault lines. Wherever you see an opening in the fault lines, that's where you can shoot it from.
If a target is available from multiple positions, in USPSA you can have a buddy stand next to it as you walk through. Otherwise, use some sort of visual indicator to note it's location.
If you see a bunch of footsteps in an area you didn't intend to shoot from... you're probably missing something.
Use visual indicators to separate which targets you'll engage from different locations. For example, from position A I will engage the target to the left of the barrel stack, the tuxedo target, and the two targets to the right of the wall... don't even acknowledge the existence of any other visible targets from that location if you're engaging them elsewhere. From position B, I will engage all of the steel and nothing else. From position C, I will shoot everything I can see.
Another thing that helps is always shooting left to right or right to left rather than jumping around in a complicated target sequence. It may technically be faster if executed well, but the best plan is usually a simple one that you can remember.