For the most comfortable viewing and best picture clarity, you should mount your LCD TV centred at the same approximate height as your eyes will be when watching from your couches or chairs. Mounting the LCD too high or too far below eye level will result in neck discomfort and a washed-out picture. If you have a large TV and plan to sit a little further back, you might want to mount the LCD a few inches above eye-level.
Angled mounting brackets allow you to mount your LCD TV tilting downward slightly. Mounting your TV in this fashion will allow you to mount it higher off the floor and out of the way while still maintaining a dead-centre viewing angle. Also, when deciding where and how high to mount your LCD TV, you need to take light sources into consideration. Never mount a TV so that light from a window or bright lamp shines directly on the screen.
Before installing a wall mount, experiment with your room set-up and screen size. It may be you like the TV mounted higher than eye level to give it more presence in your room, even if the viewing angle is not optimal. Make sure there are studs at your chosen level so you have something to bolt the wall mount into. There are no hard and fast rules. Ultimately, you will decide your ideal LCD TV location.