For planning, I usually just write down the GAP of each text and any notable features eg. specific lexical fields, first person pronouns. Once I've done the first two or three texts, I then try to identify similar features in the next texts. So if there was a semantic field in Text A, I'd try looking for a semantic field in Text D and so on. I spend about a minute annotating a text, then move on. Once I've annotated them, I flick through and try to see any interesting groupings that I've come up with and I write them down, along with which texts belong to that group - so I might write down 'Synthetic Personalisation; A C E'. It's probably best to write down your plan near one of the texts. I'd avoid writing on the front cover or by the question itself because I'm not too sure if you're allowed to write there; it's best not to risk it. I'd quickly jot down a plan by Text A.
All you need to do is keep practising! The grouping texts question is rather peculiar, so you just have to keep practising it until you become familiar.
I'm resitting this, and I don't really know what people mean when they say they use a subgroup. Like you have your overall group, do you then do another little group with the same texts or some of the same texts and another one that isn't in the main grouping?
Oh and like I've heard it's best to do 3 grouping with different texts, would you use the same text twice in another grouping?
Couldn't have said it better!!