Depends completely on the girl for me. Some girls I've dated craved it and others hated foreplay. Usually involves a lot of kissing, caressing, sexual massaging of the erogenous zones, nibbling all over her body, especially nipples and the sensitive skin right around the pussy. Depending on the state of undress at the time dry humping can definitely help get her fired up and you can kind of judge her mood/readiness based on whether she pushes back, etc. Then of course theres the usual fingering and rubbing which often leads to oral then by her begging for more.
Well, at least that's usually been my experience...