If the shelves are movable, the best option is from the sides. If the shelves are rather long, the light output insufficient and the shelves are fixed, I would try putting the lights on the underside.

The main problem is figuring out the wiring - the max run, gauge, and how the lights would be attached to the power. The power supply has to be in an accessible location.

You should be able to get some ideas from http://phantomlighting.com