Learn as much vocabulary as possible. There are lots of different websites that I used such as language perfect and vocab express (you nwill need a membership for these) and many others.
Also where possibe try to listen to people speaking spanish as it really helps for the listening exam. I downloaded some podcasts off of iTunes and listened to them which helped me to recognise some words when spoken.
You could also go back through the textbook and practice reading texts and trying to understand the gist of it instead of every word as you aren't expected to do this at GCSE.
I got an A* for GCSE Spanish and I study it at A level now. I was enthusiastic about it anyway, so I enjoyed learning. For the exam, unlike at A level, they will not present you with any vocabularly you have not seen before, so you need to learn every possible word which could appear. When I did my GCSE, there was a vocab list on the AQA website which I downloaded and learnt. Hopefully it's still there, or you could try and see if anyone on here or on The Student Room has uploaded one. Good luck!