What do GCSE Art examiners like?Watch
Try and include some observational drawing, and bits of art history/theory that relates to the projects you're doing, as this is pretty much the bread and butter of art courses in my experience (at least pre-university - not sure how it goes after). Otherwise think of your sketchbook just as a documentary book of what you are doing for your projects; it's not just for "finished" or "polished" work, use it to document what you have tried, write about what did and didn't work, and how that led to your finished and polished pieces (and where possible, try to link this to your art history work and maybe observational work e.g. X artist used this technique which I tried here but it didn't really work; however in this observational piece I used this similar technique, so I tried to combine the two and came out with this piece which worked better than the others).
CoolCavy might have some ideas about GCSE requirements more specifically? I'm a bit removed from my GCSEs (and had no idea what I was doing in GCSE art anyway - I didn't really figure things out until I started IB) so the syllabus may well have changed since, but I'm pretty sure the above is going to be generally applicable for most school level art.
As long as you are annotating everything, explaining how it "relates to my theme of ..." you'll have the examiners eating out of the palm of your hand
-Id also say to back up everything, state why it's relevant.
-Use a range of media but be subtle as well - and avoid generic themes (eg. depression, social media, weight, these all scream gcse) and don't use every colour possible on every page
-Differentiate sizes, work on large and small scales
-Show personal development and improvement. Experiment loads and record this
-Follow your mark scheme as much as you can on every page. my exam board used 'AO1/2/3/4' which was like record, develop, experiment, etc
I got a fairly good grade (8) but definitely see how I could have improved, especially since I'm doing A Level now.