http://kernelnewbies.org is an excellent resource to get you started. They recommend starting here: http://kernelnewbies.org/KernelJanitors. I would also recommend subscribing to the KernelNewbies mailing list, to participate and ask questions.

Good luck!

On and off kernel hacker here. Compile and test the release candidates Linus puts out every fortnight. When the inevitable breakage happens, use `git bisect` to track down the offending commit.

It's tedious and time consuming but you will make people very happy. The only way to test something as big and critical as the kernel is by having users actually run it.