for 'discuss adv and disadv of...' if its say 6 marks then do 3 advantages and 3 disadvantages and then say which you think are more important (breifly), try to make it balanced so like '[disadv]...causes... , however this can be coutered by... meaning that...[adv], hence ... is more important' especially if its a long answer
well im doing triple science but my board is edexcel and i only have chemistry and physics left 2 do next week.
just revise more and look at past papers and make sure your pros and cons are not too similar
grade boundaries- im not 2 sure about AQA
From what I remember, AQA have a really good textbook (for biology anyway) that tells you everything you need to know. Have a look through for the things you need to know the advantages and disadvantages of, write them down and learn three of each. If you find a question where you don't know any advantages and disadvantages, cost and efficiency are often two points you can mention, and sometimes accuracy.
In biology you might need to mention safety (e.g. if it's a question about surgery then risks of complications, that kind of thing). I can't remember exactly which topics are on which papers, but those are some pretty general points that you can use for most things.