How do I troubleshoot a failing starter on a 1992 Audi 80?

I've noticed that my Audi 80 is having trouble starting. The engine turns over slowly or not at all. I suspect the starter may be failing, but I'm not sure how to troubleshoot it. Any advice?

The first thing you should do is check the battery and connections. A weak or dead battery can mimic the symptoms of a failing starter. If those are in good condition, the next step would be to use a multimeter to test the voltage at the starter connections.