It is not a bad idea to check grammar from time to time: things we don’t remeber well, those aspects we’ve heard about but can’t use accurately… or all those structures we simply don’t know how to use. There are many books to help you do this, and also many web pages. Here we show you some of them:
English Grammar Exercises: for basic, intemediate and advanced students. It also includes listening and vocabulary practice
Grammar Challenge: fun interactive quizzes, grammar tables and an area for you to practise your written English.
BBC Learning English: Great site, tons of resources
Intermediate Level Blog 