I strongly agree with shooting .22 for practice more than centerfire. When you can report on the accuracy differences between brands of .22 you're starting to gain skill.

I was Range Officer for a pistol club's weekly shooting night for a long time. From that experience my thumbrule for pistol is that one should shoot 100 rds .22 for each 10 rds of centerfire. And shoot them all with maximum concentration.
I saw .22 shooters who were starting to show real skill develop terrible flinch with their first magazine of 9mm. A box of .22 would be required to cure the flinch.

Similar principles for rifle.