I got Joey at 10 weeks at started clicker training immediately. I don't think 8 weeks would be too early at all!
I first taught name recognition and "come". "Drop it" is another really important command and can be taught early. Sit, down, stay. Oh! Another good one to teach early is "Get your toy!" - very, very handy to use when you need to distract pup from inappropriate behavior.
"Bang! You're dead!" was another that I taught early, but only because my kids said that I couldn't!