I personally like to initiate the kiss. I usually grab them assertively, pull them in and kiss them but ease up right afterwards and let my hands linger at her ribcage, a couple inches underneath her armpits, and sensually caress them.

However, (props to G), an equally good way is Mental Kino, like joke around with her and have your face REAL close to hers, flirtatiously, this creates mad sexual tension and usually the girl will go in for the kiss, but, if you have very little rapport with this chick she'll be disgusted and push you away. Make sure she already wants you when you do this.