Choose undercabinet lighting fixtures that can be hidden behind the trim edge of the cabinetry. Measure the height of the trim from the bottom of the cabinet where you plan to attach the lighting. Choose fixtures slim enough to be hidden by the trim.
Position the light fixtures near the front of the undercabinet area. If you place the fixtures too far back on the cabinet, you are more likely to see them, because the trim isn't able to hide them as well.
Attach a longer trim piece around the bottom edge of the cabinetry if the existing edge doesn't fully cover the light fixtures. Nail the trim into place, and paint or stain it in a color that matches the existing cabinetry. Design new cabinetry with a longer trim piece if you're remodeling the entire kitchen.
Run the wiring through the wall between the studs so that it is hidden. Attach the wires leading from the light to the wall so that they stay along the bottom of the cabinet, to keep them from being visible.