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.