With the flattery, even if it's about the body (or something that she may get complimented on alot), as long as it's within the moment of notice, it'll probably be good. (You arrive to pick up your date. You knock and she opens the door.) "Hi. Wow! You look beautiful tonight!" Simple, but effective and the timing was right on. Your first look at her and you comment on it. It wouldn't be the same effect as if you picked her up, said "hi" went out and 3 hours later said "You look beautiful." She'd be like "That was nice, but why did it take him all this time to notice me?" (not always the case but some women might think that way)
As far as the flattery, it doesn't have to be about the body. Most women want you to notice just who they are. Behaviors, attitude, personality. If you're having a fun time together, comment on her smile, her laughter, the sound of her voice. "I love how you have that sparkle in your eyes when you laugh."
Say something she doesn't hear often but have it be REAL. Don't think too much, it's better on the fly. She will see the confidence and know it's from the heart. It should be a natural response to how the date/time together is. Just remember to not comment on something that she has an obvious problem with. Like if she's overweight, try not to make a direct comment on her body. (even if she has big boobs and you like big boobs. Most likely, she won't agree with you anyway) It could be something as simple as "Hey, that's a really nice shirt you have on, you give it some style." Or "Those are great shoes, where did you find them?" (What woman DOESN'T like talking about shoes or clothes ESPECIALLY when a guy gives them props for it?)
Just be yourself and have fun. Flattery should not be a 24/7 thing. Remember that you're trying to express traits about you that are flattering, and so is she. You shouldn't have to be like "I have great eyes. You think so right?" These should be things that you each pick up on together. It's just up to you to let your partner know you enjoy those little things about them. :-)