Start turning off the breaker before plugging in and avoid outlets that already have burn marks.
What usually happens is people plug in hot, this causes arcing as the metal comes into contact and starts to leave burn marks on the prongs. These burn marks act as weak insulators which increases the heat and the next time you plug in, the arcing is worse...eventually it reaches the point where you've burnt up the plug.
By turning off the breaker, there is no arcing at the plug. If you do see burn marks use very fine sandpaper to clean off the burn marks, so they don't compound the issue.
Also, keep an eye on the voltage and don't do a continuous draw of more than around 24amps. A lot of people try to use all 30amps and that will overheat things. Reality is the 30amp outlet is only rated for 24amp continuous draw.
