For subjects with a lot of content like chemistry i find detailed notes to be very useful (since if you know all the content you can answer any question basically). What I essentially did was get a ring binder and fir each sub section of the ciurse i would print out the list of things i needed to know from the spec (eg topic 1.7 acid/base you must know ...). I then made notes primarily from chemguide but also a bit from the textbook and chemrevise for more spec specific content and ensured that my notes for that section covered everything. It takes a long time to do but if you do it right yiu essentially have a personalised revision guide to revise from