For Q4+5:
- All the names of the orchestral instruments in Italian, French and German. It's not much help if you have to comment on the bassoon part and you don't know that 'fagotti' is bassoon.
- All the vocabulary lists of musical terms for Grades 1-5. I may have not bothered to learn the whole lists for my G5 as I was 13 and very lazy

but if you're looking to get a distinction then every mark counts and those are some very easy marks.
- The meaning of articulation marks (down bow, accents etc.) and words like pizz. and double stop. One question on a G8 past paper I looked at asked what + over a note in the French horn part meant, apparently it's a stopped note but I'd never seen it before.
- Notes of melodic decoration (passing, neighbouring etc.)
- Transposing intervals for orchestral instruments and plenty of practice of transposition.
- Period features and composers. I think a good way to go about this is to be familiar with some common musical features of a particular period (e.g. Alberti bass in Classical keyboard music) and then learn what eras some of the well-known composers belonged to so you can match the features to the era and then the composer. This can also help you rule out certain composers, e.g. a keyboard extract with lots of pedal and dynamic contrast is not going to be Bach. This is a tip from this website on
How to Prepare for G8 Theory which has other strategies on general exam technique and materials.
Apologies if I've missed something important which I probably have. This list doesn't include chords, intervals and other stuff you'll be covering in the harmony workbooks, just specific mark-gainers for 4+5. They're worth half the marks on the paper so if you can get full marks you're well on your way and if you know all those little bits then you can breeze through them quite quickly and have more time to take care over the music-writing questions which aren't so black and white.
DISCLAIMER: I got a bare pass for G6 theory, probably because I should have made this list before I took the exam myself! I didn't really prepare these questions properly and these are things I overlooked so I'm making sure I cover them for G7&8.