AFE book study myself first, my FI does ground school instead of flying if you want (he's being paid either way) so I then follow my self study with an hour or two ground school where he asks questions and explains stuff that "in theory" I know, but turns out, I don't always.
Then take the exam.
No fails yet, but one near miss ! IMHO, They don't have to 100%, they have to be passes.
I got a question wrong on one which led to a debate with the examiner. Can the component of thrust that causes you to gain altitude be called lift ?
Anyway, if you're FI offers ground school, I'd say use it.If he doesn't, ask him to. 1 hour ground school, 1 to 1, at £30 an hour (same as he charges for his time in the air) is worth a lot more than the £30 it costs.