I guess these are fairly obvious points, but...
(1) really know the whole Spec - especially the key terms
(2) actually precisely answer the question being asked [including describe v explain and addressing other command words like 'compare', 'justify', etc.] - as an experienced examiner I can tell you that is actually relatively rare!
(3) be careful and accurate - e.g. in graph interpretation etc. - amazing how many 'top' students lose marks on the 'easy' Qs
(4) include good geographical terms on longer answers [especially with new emphasis on extended answers] - I tell my students to re-read their answers and ask themselves "could a 10 year old have written this?" - often the answer is 'yes' - whereas a 10 year old would not include terms like corrasion, hydraulic action, de-industrialisation, rural diversification, multiplier effect, infant mortality, NICs, aquifer over-abstraction, etc, etc.
(5) similarly include "SPECIFICS" (names, dates, numbers, etc.) - especially (but not only) when named examples are asked for - case study answers must be specific to that example, not just general points (e.g. "since 1991 when Mappleton's rock groynes were built, people living down-drift at Cowden - like Sue Earle and Shawn Mars - have seen more rapid erosion of their farms: more like 10m/yr rather than 1-2m/yr before 1991") - you get the idea...
(6) link ideas together - use conjunctions like "so...", "whereas...", "leading to..."
(7) don't waffle - you will run out of time - e.g. a 4-mark answer needs 2 explained / developed points - not 3 or 4 (which is tempting when you know a lot about something)
don't leave blanks - even if some bizarre left-field Q comes up, any GCSE student worth their salt can come up with SOMETHING relevant, even if it's from their general knowledge - and if it really is "left field" (like some minor obscure part of the Spec being asked about on a 6- or 8-marker, as has happened many times in my experience), then most students will leave it blank - so any relevant point will put you 'ahead of the pack'
(9) watch your SPaG - e.g. capitals for place names
(10) complete and have marked as many past questions as possible - so that you begin to see which of these are particular areas of focus for you as a student
PS I teach my students acronyms to try and help them - RTQ for (2), PDA [pattern, detail/data, anomaly] for (3), STD for (4), (5), (6) [they like that one... a Year 8 student came up with it for me - "sir, so you want us to get STD in the exam..."]