If you're on an exam board that does set pieces you have to learn about (which I think most of them do) one of the things that really helped me was listening to them over and over while on the bus etc and really thinking about the tecniques involved as it went. So I had the clock symphony, and I'd listen and think 'and there are the stacattos', 'there's the change in dynamic','there are the brass'. It helped me have specific examples when writing about it