Some things to try:
1. Check TVFool.com for his exact location to get compass directions for TV towers.
2. Aim the antenna at that compass heading, check signal strength.
Move antenna left or right a degree or two and compare signal strength.
As some stations are not line of sight to your location, you get better reception with the antenna not pointing directly at the tower.
Keep moving the antenna until the signal drops off then try the other direction until signal drops. Somewhere in between will be your "sweet spot."
3. Move the antenna down on the mast, if possible. Sometimes pointing under the trees is be better that aiming through them.
4. Tilt end of the antenna aimed at the tower up a bit, if possible. The horizon might not be horizontal at his location.
5. Remove splitters, combiners, other antennas, etc. and use a single run of decent coax to the TV/converter to start.
6. Might need a bigger antenna.