I suppose you might get a better response in the D&G forums. I presume you have time or budget limitations and so here we go:
Go to class for Flight Planning. It's hard doing it on your own.
If you are reasonably confident and disciplined with self-studing, you could include Perf & Loading, Aero & Systems and Nav. Otherwise go to class.
The average person should not have problems with Air Law, Met or Human Factors.
I self-studied and passed all 7 - proves it can be done. Good luck.