IMHO, met and nav were the hardest topics until you actually do some flying, then they're no problem.
If you're already planning XCs with a plog, Nav ceases to be an issue.
Human Perf is simple - less than O level biology really, and Air Law is a just an exercise in memory.
If you've just started theory, then it's unlikely you're doing XC's as you'd likely be doing AirLaw first to go solo (if you're in the UK).
The AirLaw "requirement" isn't a legal thing, but no club will let you go solo without it, so I'd start there. Once you're doing solo navs, Nav becomes fairly easy provided you can use a whizz wheel and do a proper plog. Met also benefits greatly from a bit of experience.
If you can afford/get them, the Oxford CDs are good - they cover the main points quite succinctly. If you can get hold of a confuser/Simplifier - even better.
Personally, I preferred Thom over Pratt, but Thom is quite wordy - depends on your preference.
Watch AirQuiz - they're good, but some of the questions are ones you'll never be asked in the actual exam, and they can be quite a bit more complicated than the exam questions - that being said, if you're scoring pass marks with airquiz, and understand the topic, you'll have nothing to fear!
