Most break-in tips are mainly recommended for the first month/100 hours; after that just don't abuse the set (ie. leave an image on pause for 48 hours) and you should be fine.

Don't crank the brightness to max. Keep it at a reasonable level.

If it has an auto-wide mode (stretches 4x3 to 16x9) and you watch a lot of 4x3 SD, use it.

If it has an anti-burn-in mode (something that subtly shifts the picture around), use it.

Plasmas are not nearly as sensitive as they use to be (in fact the general claim these days is they AREN'T sensitive). Beyond the obvious, there's really nothing to do or worry about.

I've had a Pioneer PRO-150 for a few years now... best set I've ever owned, and zero signs of burn-in or uneven phosphor wear.