Their is no set formula for guaranteeing a place at any university, they judge and value each candidate on a number of different factors. Law is an incredibly diverse subject and so their really aren't any set a levels which will directly hinder/ improve your chances. Personally I think that universities are more bothered about your interest in the subjects and what intrigues you as opposed to masses of work experience (although it is definitely still worth getting some and referencing it). Each university and admissions team just differ on what they look for. My AS grades weren't particularly outstanding and I only have 1 day work experience in a law firm yet i got a reduced offer from Nottingham but was rejected from Manchester which is considerably lower in the tables. So don't worry if you're lacking in certain areas and don't be cocky if you're excelling because I've seen straight A* grade students be rejected; it all depends on the individual student and application!