Outlets and ports for data, phone lines, cable services, and/or power should be at an easy-to-reach height, meaning that there’s no requirement for someone to bend over significantly to access them. Between 16-20″ from the floor to the bottom edge of a cover plate is ideal, but no higher than 48″ to keep everything within a reasonable reach range if a lower install isn’t possible in some locations.
In stairwells, it’s nice to have power at the top and bottom to increase flexibility for vacuuming or installing a stairlift if needed.
For kitchens, bathrooms, or other spaces with counters, make sure outlets and ports are at least 20″ from any corner for ease of access. Depending on layout, mounting outlets or switches near the front of a counter may be useful as well.