I did well at French GCSE twenty five 
years ago but now I'm out of practice. I'd like to revise what I used to know then try to move on a bit.
I don't want to start from the beginning with a teach yourself book, but doing Duolingo I'm clearly missing some essential grammar that has fallen out my ears at some point.
Can anyone recommend something to help me do this? I was thinking a GSCE revision book might do the job? Or is there something else?