If you are looking to study at university in the UK (or any other English speaking country) then this free course from the University of California might be useful to you. There is an OPTIONAL $50 fee if you want a certificate, but getting the certificate doesn't increase your chances of being accepted into a top university.

You can find the course here;
https://www.edx.org/course/english-grammar-essay-writing-uc-berkeleyx-colwri2-2x-0

It is taught by respected lecturers at a top American university. Don't forget if you want to study in England there are small spelling and colloquial differences.

If you want anymore help to apply for a top British University then have a look at this website;
http://ukapplications.wixsite.com/britishuniversity