1. Know your pieces. If you have set pieces, make sure you listen to then over and over again until you have a complete idea of the structure, any of the main features and characteristics - know exactly where they occur and what instruments etc. are playing where.
Tools: mind maps, cue cards with bar numbers on, Annotated scores (in colour) and power points.
If you need to learn a specific ABAC etc. structure, create colour coded cue cards with each section letter on. Listen to the music and hold up each card at the correct section in the music.
Create a table summarising each section of the music. Keep the notes short and use key bar numbers. Learn this table and then try to recreate it from memory.
2. Practise. Do all the practise papers that are available to you. If you have essays in your exam, ask your teacher to give you more questions to do and hand them in to be marked. Do them under timed conditions.
Look at example essays and compare with your own analysing what you could have done differently.
Good luck for exam period. Don't give up it will be over soon. Make sure you revise until you can revise no more.
Would anyone be interested in some A-level music resources if I was to upload them to my blog?