Hi, I didn't do A levels, so I can't give you any detail I'm sorry, but I can tell you about LNAT and Personal Statement
For the LNAT, some schools use it as a very qualifying factor, some put less importance on it, while others don't use it at all. You really can't prepare for it, all you can practice is maybe the skills like time management, reading between the lines and concentration. So I advice that you become aware of your deadline and fix a date where you're mentally and emotionally ready for it. If you're going to apply, pick schools that use LNAT and those that don't just to be safe, and when picking LNAT schools, try to pick at least one that admits many students, that way even if your scores are not so good, you have higher chances of getting in because there are many places.
As for personal statement, you basically need to sell yourself. Talk about what inspired you to study this course, what skills you have that will enable you be a successful student, what you plan to do with the course, etc. If you're going to apply to LSE your personal statement needs to be gold because they don't use LNAT, so once they don't like your PS you won't even move to the next stage. You can always ask trusted people to go over your personal statement to find out if its convincing enough, but ensure that you don't copy or use too much of other people's input, so you don't lose your voice. Hope this helped.