Apart from passing the Life in the UK Test, you may also have to pass an English test to prove your level of English is at least B1 Level. B1 is Intermediate Level. There are some good sites on the internet where you can practise your English.
The Exam English website is one example of these.
Grammar Bites: Great site to practise grammar.
Here is another free resource for learning English. The website is from Thailand so the examples are of US English but still very useful for us here in the UK!