I attended an online course on leaf-mining, yesterday. It was delivered by David Slade, the County Moth Recorder for Glamorgan (VC41). It's about an hour-long presentation, plus questions, and - I thought - serves as a great introduction to the subject, with some very clear pictures to show what to look for in some of the commoner species. Here's a link!
https://www.youtube.com/watch?v=G4nGikR ... ex=11&t=5s