There are a couple of things you might want to try..
First, Thinker's suggestion is the best, but you first have to _find_ good players, then look for them next time you play. If I play someone good, I'll add them to my friends list so I at least know if they are playing in the same room. I only wish the friends list had grouping.
2nd, specify in the sets, good players only. Yes, this will be ignored sometimes, but the average newbie doesn't want to get squashed like a bug either.
3rd, play with sets that newbies will tend to avoid. I have really gotten to enjoy a random-nomad start. Most newbies will avoid these games like the plague. If someone comes in the room and asks what nomad means, you at least can then ask them what kind of player they are. I don't believe in just "booting" someone, so I would ask them if this is really the game they are interested in, and maybe suggest they find another game.
You will find it harder to get a game started using options 2 & 3, but the games will be much more enjoyable.