Law only vaguely comes into one section of most AS Politics courses: the judiciary. Other than that it's very different to Law. Psychology is probably important if you might want to study it at university because it's such a competitive course, but any combination of the subjects you're considering will be absolutely fine. Sociology and Politics could compliment each other nicely, but you should just pick what you most want to study because the best grades are what universities look for, not so much the subjects unless you're looking to go to the elite unis which are extremely selective (Oxbridge, Durham etc.).