podszkolić się Englisch:

Instead of wasting my time, I should brush up on my English more often

(inseparable): review / study thoroughly for a short time; "If you're going to travel to Peru, you'd better brush up on your Spanish."

You'd better brush up on your spanish.

„Instead of wasting my time, I should brush up on my English more often”

We’re going to France for our holidays, so I’m going to have to brush up on my French.

Mary decided to brush up on her Spanish before going to South-America.

If you're going to travel to Peru, you'd better brush up on your Spanish.

You might want to brush up on the traditional police work.

I'm going to have to brush up on my spoken German.

I need to brush up on (my English)