How can I prepare well for a MSc in the UK?
Here are a few tips if you want to be proactive:


Find out what topics will be covered in the course, and start reading some of the topics which interest you.  See if there are any websites on the university that list the topics offered, and if you can access any of the learning materials.
Reach out to some the professors and start talking to them.  (This will also be helpful later when you select a thesis)
Reach out to previous students; ask for previous years' books and materials.  (Tip: There will probably a facebook group for everybody that does the course for a given year, ask someone to add you to the previous year's group)


But remember, as I mentioned in the comments, in the UK the independent 1-year master's degrees are set up primarily for foreign students as an income stream.  I saw this first hand when I did a master's degree in Oxford.  It is not good for business for them to fail students, so there will be a lot of support available.  So while there is no need to become complacent, I wouldn't worry too much.