do it with meaning...don't just do it because you can...but because you want to and because you value her (and make sure she can feel it in the kiss)...
try turning your head to the side a little and going in for it...kiss her lightly and make sure your lips are nice and soft (and that your kiss is the same)...
i'd agree with the beautiful comment thing from swingfox...but something i like to hear more than that i'm beautiful is that i'm incredible or amazing...