Why painting a bathroom is different than painting a bedroom:
Paint in bathrooms is frequently exposed to moisture. You'll want to use a paint with some sheen to it to minimize the exposure of moisture to underlying substrates.
Bathrooms are the #1 area where we see peeling and bubbling paint when doing interior paint work. Depending on the extent of the peeling, you may need to mud peeled areas with joint compound in order for the final finish to look smooth. In some cases, sanding the area is sufficient.
Color selection: As a rule of thumb, it's best not to paint small rooms (such as bathrooms) with a dark color because dark colors make rooms look smaller. However, a well-lit bathroom with bright vanity lights can counteract the effects of a dark color.