Get your papers ready (passport, visa, letters from the school, study programme etc.) - put them into your hand luggage NOT to the checked-in baggage as you won't have access to them when you will need them - immigration control is before the baggage claims.
Memorize as much about your study as you can - where you will be studying, where you going to stay, what is the course of your study + details about it, what you want to do in UK in your time off - work (part time only - 20hrs max.) etc.
But don't learn it as a "poem" or totally automatically as the ECO the entry point can sense it and be nosey - it is much better to be just yourself, natural and relaxed as Ann pointed out.
No need to worry too much about it, I know you will be all right and that you can do it.
Wish you good luck
