I've found that for most girls when they are still warming up, too much contact on the underside of their lips is just too much stimulation. Until they get really ramped up, just bring her to minor peaks by lightly running a finger(wet) or tongue over them then back out, say back to the inner thigh for a sec. If it's wet enough blow lightly on that trail back to her pussy.
Gradually escalate, based on her body cues.
As for the clit, girls vary WIDELY on how sensitive it is, and that sensitivity also varies on how excited they are. There's no harm in asking about it, if they don't already indicate to you their preference.
The "come hither" thing works great, and there's a spot above it, where if you reach in as deep as you can (two fingers seem to get further) the tissue gets harder. (I would say about 4 inches in) If you use the same motion there you'll get a great reaction. it's almost like a second g-spot.