You don't need to do any SAT IIs in Maths unless you're applying for a programme that specifically asks for it. That being said, if you are planning on taking Maths, definitely do II, because a lot of good universities seem to consider Maths I as a bit lightweight. If you could do better it might shore up your SAT I Maths score, though.
I did World History and Literature, and honestly there isn't really any way to prepare for Lit short of doing a few practice tests. If you did it in 6th Form you should be fine. World Histo might be an issue, though; it's very, very varied, so I'd recommend you get one of the booklets of official past papers and fine out which areas your knowledge is lacking in. Given the fact that it doesn't conform very well to the British education system, though, you get some latitude on the part of receiving universities.