After going through teh application process I think these tips should help people not get the same problems I did.
1: Mention the specific degree you apply for and explain why you want that specific course (Mphys F303 and not merely Physics). This shows that you have thought about what you want to do and that you are applying for the same course at all unis, which in turn means you are determined to stidy that course.
2: Mention what you want to do after obtaining a degree. This also shows that you have thought about your decision.
3: If you have some working experience or other extracurricular experience which could help in your study, then mention it. As an example, if you apply for a Maths degree, make sure to mention the programming you have done as a hoby. Remember that most unis do not have interviews, so if you dont tell them they woant know.
4: Explain why you have applied for teh course you want to do, but avoid obvious ass-kissing and clisheys. Dont give the people some fantastic story which spielberg would love, tell them what you like about the subject.
5: Remember that these peopel have to read quite a few applications, so dont make them read the same phrase for the 3045th time. If you start your internal assesment with "The reason I picked History..." they will have read a few hundred of those statements already. Try to be original, but use your own words.
6: Make sure the person reading teh statement remembers you (not in a bad way though). If you have the guts you may insert some funny quote or a small joke, just make sure it is not anything which is going to be reacted on in a negative way. Had I written my ps today (applying for physics)I would have inserted the monthy pyton quote "And so we know that the earth must be Banana shaped" - Sir Bedevere