If you've never faced him before, watch his practice swing. The practice swing will tell you what location he likes the ball. If a left-handed hitter comes to the plate and he takes a practice swing at what would be a low inside pitch, you can bet that's the pitch he likes to hit and will be looking for. Try to start him out with a fastball out and up. When you have faced the same hitter more than once, you will have some experience to draw from.
Good hitters adjust very quickly to a pitcher.
That way you can give that hitter 3 different looks with just your fastball. Make the hitter uncomfortable. There is nothing that makes a hitter more uncomfortable than knowing he can't handle the inside heat or that he has to commit himself early to hit this pitch. We're not talking about knocking the player down or brushing him back, but establishing the inside part of the plate and letting the hitter know that you will throw there. Make the hitter change some aspect of his swing from the pitch you just threw.