My son is at Highgate and although it was 5 years ago there are a couple of practical tips that he found useful in the final stages of preparation (he had a tutor with whom he did past papers, no books btw). As stated on the front of the paper, the Maths paper has to be completed a page at a time - they tell you when you can turn over and you can’t go back, so he needs to be prepared for that. DS also benefitted from being told what I thought was obvious

- that its important to get the easy questions right! Take plenty of care with those, he thought it was more important to impress with the hard questions! There is a Bond book called How to do Comprehension (or something like that) you won’t have time to go through it now (and I didn’t with DS) but it does have a section which goes through a paper and shows a poor answer, a middling answer and a top marks answer for each question. DS found it really helpful to see that and to see how you get the examiner to give you top marks. Being a more mathematically minded child I helped him devise a way of writing a story with a plan (first para introduction, second action and third ending) and to think punctuation (try and include speech or thoughts) and senses/description.
Good luck!