First off, although often just referred to in aquarium shops as 'bristlenose catfish', there are actually over fifty five species. Many of these can only be distinguished from one another by close examination, so if you want a breeding pair it is safest to buy two at the same time. A lot of plecos are hard to breed, but bristlenose's have been bred commonly in home aquaria.
The best crevices for potential spawning sites are long narrow ones, and plastic or bamboo pipes can also be used to provide shelters (which will eventually become spawning sites). The male will find a crevice to call home quickly, and thereafter will usually be found there. In contrast the female is more nomadic, and does not set up home in a specific spot. Unfortunately bristlenoses are not all that bright when judging the width of a hole, and care should be taken to ensure the provided decor is free of hazards.
Unless you are collecting bristlenoses and particularly want a special species, the best buy is four or five of the little 'tank bred' fish (usually Ancistrus sp. '3'). These are likely to grow up into confident fish that are seen out and about in the tank, and will spawn successfully in your water (bright orange eggs).
its best to have 4-5 of these, only one being male-the stronger will eventually kill any other males unless in a big tank.
22-24 degrees C, maybe towards higher for spawning, with a pH neutral - slightly acidic. (mine bred at 6.5)
information
http://www.planetcatfish.com/cotm/1998_12.PHP, and google bristlenose catfish breeding, and should get lots of hints n tips.