keep your hand in

mainly UK

to practise a skill often enough so that you do not lose the skill

经常练习(以免技艺荒疏)

I do a bit of teaching now and then just to keep my hand in.

我有时教一点书，只是不想让自己荒疏了。

I also did a bit of book reviewing to keep my hand in.

我还写了一些书评，免得自己生疏。

You should at least work part-time, just to keep your hand in.

你至少应该做一份兼职工作，免得生疏了。