First think about where you need the highest levels of light to see what you are doing, then put a light source there. The most common practice is to mount fluorescent tubes along the bottom of the upper cabinets. This is an effective approach but not the only option. A technology rarely considered for this application, but which has definite benefits, is fiber optics. Fiber optic strip lights, for example, give off no heat at all.
Fiber optics works by carrying light along hair-thin filaments of glass.
This installation makes changing bulbs or repairs delightfully simple. With under-cabinet lighting, be sure to consider the nature of the surface material it will illuminate. If the surface is glossy, as in stainless steel and polished marble or granite, the counter will become a mirror reflecting the image of the light source. Always bring the fixture forward and block the face so it doesn't shine in your eyes when you sit at a nearby table. Suppose you need light on a countertop where there are no upper cabinets.