Hey, I did GPR last year at a grammar school. The only tips I can think of for the presentation is to get others to read it through to make sure the argument flows and makes sense etc, get a range of materials rather than just one type of source (gives you more to critique with) and if possible, get a teacher to check it through to make sure it's done correctly (I believe it can only be checked once though). Biggest tip is don't record it on the very last possible day, we all did that at my school and it was a very stressful experience! You'll find GPR is so useful with uni offers as you already have one a level equivalent under your belt and can affect offers (Exeter lowered my offer based on GPR). Good luck with it all!