"Brush up on your skills"

[emphatic]

Growing up in the 80's with an arcade (2 cabs at least) close to home, I went there whenever I had pocket money to spend. There were a stream of golden age classics in this place, so I tried to play 3 credits on both cabs whenever I visited (the third credit had a discount price).

I quickly got better every visit, but not always from each credit to next. So my advice is:

Play more than 1 credit every session, and make it matter. Hey, perhaps it's not a high score run, but at least you'll learn the power up system, or enemy behavior etc. Then switch to a different game during the same session (unless you play PCB only and have only one cab) and play a couple of credits on that one as well.

You should get better on one of those game at least, and you can then choose to concentrate on it, but it's more fun to change it up a bit IMHO.