Measure wall width and ceiling height where the item will be placed. Do not count window or door moldings, measure from outside of these. Also, when considering depth, measure along the floor from the edge of the base/shoe molding, NOT from the wall surface. If the unit is very tall, measure from the edge of the crown molding instead.
If you have wood floors, you may want to consider a contrasting color for your wall unit.
Buy the TV you want first and then find a wall unit to fit; else take the actual measurement of the TV cabinet first before shopping for a wall unit. (You want the actual width and/or height of the TV cabinet – NOT the screen size)
Most entertainment centers are made without doors now that TV’s are getting wider. Many have doors that open wide and/or wrap around the side of the unit. Be sure to allow clearance from walls, windows, doors, and other furniture to open the cabinet.
Make sure the proper connections are available on the chosen wall. (cable/satellite/antenna feed, audio jacks, sufficient AC power outlets, telephone jacks, etc.)
If you will also be storing video and audio components, measure width, height and depth of each to ensure a proper fit in the cabinet with enough clearance for wiring in the back.
Curio display cabinets come both with and without lights. Be sure to have an available power outlet if you want one with a light.
For books, measure the tallest and deepest books that will be stored on the shelves to ensure proper fit. Some units have adjustable shelves, some fixed, and some both.