Manual just takes practice, there's no way around it. This it the first year that I have everything on manual and I am loving it. Once you get good at manual passing, you might actually be better than with assisted. On manual, you can put a pass right where you want it, where with assisted the game tries to guess where you want the ball and player to meet (sometimes poorly).
I started in stages. First I did manual passing, then shooting, then finally through balls and lob passes. There will be frustration at first but eventually when you get the hang of it, putting together the perfect scoring play is just that much more satisfying.