If you don't already have a fireplace, decide where you would like to put one. It's a good idea to contact a contractor who can help you figure out where the safest place will be.
Figure out how large your fireplace will be and how large of a television you'll have. If the fireplace and television are disproportionate, it may cause scale problems for the rest of your room. Use painter's tape to test different dimensions on the wall above your fireplace.
Do the math to figure out where your television will hang. According to ApartmentTherapy.com, "Depending on the height of your mantel---or if you don't have one, the top of the fireplace---hang the TV four to 12 inches above. If your mantel is higher than four feet, then hang the TV no more than six inches above."
Hire an electrician to give you a quote on the cost of hiding the wires of your flat screen television. Hiding wires will keep things looking neat and seamless.
Decide if you want to create a seamless flow from fireplace to television. You can do this by using one piece of material (wood or metal) to build a frame around both the fireplace and television for a more modern approach.
Invest in a tilt wall mount, so your TV can point downwards. Some people believe that mounting a television above a fireplace makes for uncomfortable viewing. If you use a tilt mount, you will reduce strain on your neck.
Above all, go over your plans in detail with an experienced contractor to make sure that they are safe. A fireplace is a cozy addition, but without the right ventilation and precautions, it could be a dangerous one.