I started taking a heavier interest in clang-tidy a few months ago, as I was looking at static analyzers. I found at the time that it was quite complicated to work on clang internal AST. It is a wonderful tool, but it is also a very complex one. Thankfully, the cfe-dev mailing list is full of nice people.
I also started my journey in the LLVM/clang land with the help of this blog post.