In general bristle worms are a good thing. They make brilliant CUC as they can get into parts of the tank that snails and hermits cant.
If you want to thin their numbers out though there are things you can do.
The best way (but most time consuming) is to get some tongs, drop some food in the tank and then remove them manually. This is hard though as they are quick little buggers.
Some Wrasse will eat them (apparently but not seen this firsthand).
Take a bottle and make some smallish (worm sized) holes in it. Put a bit of food in there and leave it in the tank over night. You will get a lot of worms this way but don't use too much food or leave it in for too long or you could foul your water and have an ammonia spike.
I've seen my sixline take a stab at every bug imaginable. He completely decimated my bristle worm population as well as my copepods, peanut worms, etc...
My cleaner shrimp are bristleholics, all three of them team up to shred even the big worms.
That said the 3 lads will try to eat anything the first time they see it.
Thanks guys I got a spotted hawkfish for eleven pounds from my LFS and he has nearly bamished them from my tank except he is attacking my damsel so I am trading him in!!