Before coming to UK, there are a lot of things you can do to help you make the most of your time in the country.
Listen to British TV and radio stations. This will help you get used to the sound of English. Don't worry if you don't understand everything. The important thing is to hear English. After a short time your brain will start to recognise the sounds of English better. You can download programmes from the BBC.
Watch films in English sometimes with and sometimes without subtitles.
Select some photographs of your family and your town/city which you can bring to UK. Practise talking about them before your course so when you are in UK you can talk about them with your teacher!
Try to read some simple books in English (you might be able to buy reading books specially written for people learning English). You don't need to know or check every word in a dictionary. Try to get a feel for the most important words or expressions in English. If your level of English is already quite good, try reading newspapers or magazines.
Find out a little about British culture and what is happening in Britain at the moment. The BBC is good for this.
Try speaking to yourself in English. Even better, find someone to speak English with! This will give you practice moving your mouth in an English-speaking way!