What book did you read? It helps to mention it and a specific part of it, something complex preferably.
Reading outside the A-level course is very useful and attending lectures is really good.
If you want I can PM you my personal statement for Maths but the TSR bank has better ones, especially the Oxbridge ones. It's always good to look at the best and take from them.
I wouldn't talk about graph sketching, multivariable calculus is a good one though.