Your personal statement is an essential part of the UK university admissions process, and something you really want to get right. A good personal statement will demonstrate to the Admissions Tutor at your university of choice that you are enthusiastic, able, interesting and multi-faceted. If you're applying to Oxford or Cambridge it's vital to getting an interview, and probably just as important as your predicted a-level grades in the final analysis - since, whilst many people will be expecting straight 'As', fewer will interest the tutors in their statements.
I only really know in detail about a personal statement applying for English, but there are some good general rules:
- don't go on too much about how you captained the third XI cricket, or whatever. Unless you've done something fairly outstanding in your field - like captained the school and played for your county, for instance - keep the reference to it brief. Principally they're interested in your mind.
- Don't be pompous. Don't be afraid of sounding excited about the possibility of studying your chosen course at university: they won't be impressed by you being laid back and cool.
- The main body of your P S should be an explanation of why you're interested in the subject and a list of interesting books you've read related to the subject. This should account for, say, 7/10 of your 33 lines. That's true for arts, anyway: I'm less sure about sciences but I imagine much the same thing applies.
- For English, at least list a selection of books with a wide chronological spread: don't make it look like you're a dilettante. Similarly, with History, it pays to have read outside your a-level syllabus, and to show that you're interested in the subject in general and not just, say, 18th century France.
- Don't lie! And don't put anything you intend to read but haven't quite got round to. If they catch you out at interview YOU ARE FUCKED. Not worth the risk.
- Spelling mistakes are also the kiss of death. If you can't be arsed to proof-read the thing properly, you don't come across as very enthusiastic. Remember, they have so many applicants that they're looking for reasons to drop you, not reasons to keep you.
That's about it. Ask teachers for suggestions for reading a good while before the deadline so you can get it done. Good Luck!
(If anyone wants to read an example P.S. for English /msg me and I'll e-mail it to you) | 
