There is no rule such that the bathroom lighting should be provided only in the ceiling or is better if it is provided at the sides or on top of the mirror. One has to fix the bathroom lightings according to one's taste and the mood that he or she wants to bring into the room. Even for a small bathroom, people, these days, go for two or more lighting fixtures. Thus, lighting is the most important factor to be considered in any modern bathrooms.
There are lots of varieties and styles of beautiful flush and semi- flush ceiling mounts of bathroom lighting fixtures available in the markets, which will go well with the mood of any bathroom.
If you want to look your best then you'll probably spend a fair bit of time in the bathroom, but unless you have decent bathroom lighting you may not be seeing yourself in the best light.
The different varieties of lighting fixtures include ceiling fixtures, side wall mounting fixtures, etc can be chosen as per one's taste and requirement for his or her bathroom. Also depending on the size of the bathroom, one can choose from a single light fixture to a couple or more lighting fixtures.