Help with Reaction Time and wave?

I can't play right now since I'm outside and got bored. So I got some questions that might be obvious to most people here.

My reaction time is horrible since I rely a little too much into memorization and timing. How should I improve it in general?

The things that came up in my mind is just playing easier levels without using practice mode unless something is confusing, what else can I do? Or is that pretty much it?

And also, wave. I think an obvious gamemode that relies a lot on reaction time is ship, but what about wave? Should I follow the icon as it frantically moves up and down, but how am I gonna react when I'm looking ahead? Or do I look at exactly the middle of the screen or something?

Am I making things complicated? I got the dedication on beating levels but I think I might be stupid for relying too much on memorization and timings without noticing until now.

I know that it gets better as I play more levels and so on but if I can improve faster by knowing how to focus on my weaker skills, why not?