GCSE art - tips?

I didn't. I was over ambitious with what I could do and ended up not even having free time during holidays to relax, but had to do art. I was always praised for my paintings and artworks, they had meaning behind them, however because of my sketchbooks being almost empty (I couldn't finish them) my grade was capped at a 6. You need a healthy balance of sketchbook & artwork - remember, examiners don't necessarily care about your skill too much but the thought and process of developing each painting. Also don't bother decorating your sketchbook. You can add images and make it cohesive and maybe even some extra colours, but don't make the mistake of spending to much time on it. Put all your creative effort into the artwork and all your mental effort into the sketchbook. If your priority subject is art, focus on it.
Also you have to do extra work and extra experimentations, etc.

What my school did is that deadline isn't 100% - we were still allowed to take books home during the holidays and complete them (however the teachers had to tell the examiners that you went past the deadline)