Pay attention to your appearance.
Let him know that you like him by making an effort to look nice whenever you're around him. You should still be yourself, but take extra care with your hair and makeup and outfits, so he can start to notice you. You don't have to wear a tight dress and high heels if you're at a baseball game with him, but let him know that you care about your looks when you're around him..
Don't be afraid to be a little sexy. If you're comfortable with your body, show it off.
If you're not comfortable with a lot of makeup, then you shouldn't try to look like someone else just to impress him.
Try wearing a little lip gloss, and applying it in front of him. This will make him pay more attention to your lips.