1. Make sure you have good ventilation around the plasma - as with any electronics device, it needs to be able to circulate cool air around it. No tight enclosures.
2. I personally avoid displaying 4x3 shows on my screen. I think it is a good practice. Watch 4x3 programming in stadium or stretch mode. It fills up the screen and provides no border for the screen to burn into. If you have a show that you can't stand to watch in stretch/stadium, then go ahead and watch it in 4x3, but if available, change the borders on the plasma to grey to help avoid burn-in, then go back to stretch/stadium after that show is over. A few hours in 4x3 mode won't cause burn in... constant 4x3 will.
That's about all I can think of that I am doing to keep my plasma going and it seems to be working so far. In 100+ plasma installations, I have seen them blow out more from 'custom' wall mount jobs that havne't provided enough ventilation, than from burn in issues as most people want to fill the screen with video and that goes a long way to protect the screen.
