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.
It is wise to use flush-mounted ceiling fixtures, owing to the fact that these come with bulbs that are enclosed by a kind of cover. The cover is essential as it acts somewhat like a lamp shade and helps in diffusing the light as well as protecting hot bulbs from breaking and cracking from contact with water vapor. The best would be to have the right balance of ambient bathroom lighting and task bathroom lighting. This will give your bathroom proper illumination and make your bathroom experience worthwhile.
But the second aspect to consider when choosing your bathroom lights is safety. Clearly a bathroom is a wet area, and electricity and water are not the best of companions. Today however there's a very easy system in use which helps you to quickly and easily identify the type of light that's suitable for each area of your bathroom.
It is indicated that you should use lighting fixtures directed down with special ornaments or decorative pieces which help in reshaping the bathroom and obtaining a special effect. Sources of lighting must be fixed and directed so to have an efficient light and to focus on dark areas or objects that you want to put in a special light.