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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)

I need to brush up my Spanish.

He went to Canada to brush up on his French before the exam.

He went to France to brush up on his French before the exam.

I will need to brush up my English before I go on holidays.

There was no time to brush up on the language.

I want to brush up my English.

brush up on Maths

I think I should brush up a bit on my Japanese before visiting Osaka.

I need to brush up on my Spanish, because I had quite a long break

So, brush up on the English that you started learning long ago, or start learning today.