I've recently run into several cases where a fixture was burning out its bulbs in a matter of weeks, or even days. In one case, I was told that swapping the 60 watt bulb for a 15 watt bulb made it last significantly longer.

I'm at a loss as to how to troubleshoot these cases. Where do I start? Do I look for loose wire connections, faulty sockets, or what?

Thanks in advance,