Use a stud finder to locate the studs in the wall where you would like to mount your TV and use a pencil to mark their locations. Determine which stud(s) you’re going to use (depending on the size of your TV you may have a single-stud mount or a dual-stud mount) and mark them with your pencil.
Line up your wall mount on the stud(s) and use a level to make sure it's straight. Mark the screw holes with your pencil, set the wall mount down, and then drill the screw guide holes with a power drill.
Place your wall mount back on the wall over the guide holes and use your power drill to anchor it to the stud(s). Anchor screws are always included with wall mounts, so find these in the wall mount box.
Secure your TV to the wall mount using the screws included in the wall mount package and then adjust the tilt of the wall mount as necessary to offset the slant of the wall. Route the cords for the TV as desired and connect your devices (cable box, DVD player, etc.). Your TV has now been successfully mounted to your slanted attic wall; use a shelf or stand to hold any devices connected to your TV.