Good thing about Law is they like people from all different academic backgrounds!
Essay subjects are always appreciated, so English, History, R.E/Philosophy.... But apart from that you can pretty much take what you want as long as they are considered 'good' subjects. So best to pick what you're good at and/or what you enjoy! Sciences are also good, shows an 'analytical' and 'logical' mind which they quite like, so if your okay at maths it might be a subject to consider.
So English, History, RE, Maths, Bio/chem/physics,psychology, philosophy, politics, Economics, Business, geography, languages (I'm sure i've missed some...)
Bad things to do would be for example:
o) Both Buisness studies and Economics
o) More than two 'soft/arty' subjects like Art, Textiles, Music, Drama, Media, journalism, etc
o) Avoid Law A level. even if you want to do law it doesn't go down too well, lecturers say they have to correct everything that's been taught at A-level and some consider it a soft option.
o) Of course avoid critical studies/general studies unless it's an 'extra'