Patch it like this..... http://www.youtube.com/watch?v=LsX26bQ53sQ
If its small you can do something like this, pretty much just fluff it.
The method I seen is just cutting out the burnt part then find a place in your house with carpet that really isnt notice able if it went missing. Cut it a piece the size of your burn and just super glue it down. *Probally the easiest thing*
But the best best best thing to do is just where ever you smoke put down an area rug. Just today my cousin dropped a coal and it burnt almost through the rug but it would left a hell of a burn in the carpet if that 30 dollar rug wasn't there.