First off is an obvious one that you should already be doing, if not be seriously considering doing right now.
That is making flashcards using your revision guide AND also making sure to review them on a regular basis - this will help you to fill in any gaps in your knowledge that have occurred over time.
I would highly suggest using Anki (a popular flashcard program which I HIGHLY RECOMMEND) to do this, though the same can be achieved with paper flashcards as long as you keep up regular practice.
This is an example of ACTIVE RECALL & SPACED REPETITION as not only does it force your brain to think through to the answer that's on the back of each flashcard, but in doing so (given you keep up regular practice) ensures that it will re-jog your memory when you are just about to forget what you've learnt.
In addition, I would also like to mention an up-and-coming revision technique that has become really popular in recent years: that is, of course, BLURTING. Blurting is a technique which involves writing out notes/drawing mindmaps from memory of certain topics you wish to revise. This can help you to really visualise any gaps in your knowledge - especially if you draw mindmaps!
Now I'll admit, when I initially heard of this strategy, I myself wasn't too keen on it as it seemed like tough work to me at the time. However, I was willing to change my mindset and give this a go - and it has worked wonders for me in my revision. Not only does it make it easier for you to find holes in your knowledge, but it also further cements the very information that you are trying to learn - which is exactly what you need to to in order to achieve those 8's and (in your case) 9's!
Once you are more confident on your core knowledge, make sure to go through SOME past papers, though not all since there is only a limited number of them.
Attempt the papers (in timed conditions if you can, but if not then fine), then try to mark yourself using the mark scheme - pay close attention to the wording on the mark scheme, as this will really help you to perfect your exam technique.
These techniques helped me to achieve grade 9s in Combined Science even with very little time on my hands, though these very much apply to Triple - if not moreso than Combined, and may also take you a little while longer to do, but will very much have been worth it in the end.
However, your mileage may vary which is why I would recommend doing this over a much longer period of time (say 4 or 5 months leading up to your GCSEs) rather than just 2 or 3 months, which trust me, will ultimately leave you stressed and in a hurry - meaning your revision may not be as effective as you will be cramming in loads of information at once as compared to doing a little bit every day so that your brain will have the chance to process it and retain it for much longer.
Hope this was helpful.