Lips are naturally suggestive, bringing to mind images of intimacy and attraction, and thus are powerful amplifiers of unspoken language.
Light licking or soft touching to your mouth area can catch their attention, creating a cue that you are attracted to them and may want to progress the relationship further. That little, almost subconscious gesture can be a verbal-free, intimate scene.
The best way to employ this technique to its fullest is to moderate. Do not overdo it, that may get you in the reverse direction making you look like a person who is conscious about himself/herself or may be making appearance with a lot of hard trying efforts!
A simple, genuine gesture, perhaps when you make eye contact or while you are listening to them will cast a spell of mystery. A fleeting glance can be communication in itself, the way that your finger lightly touches your lips speaks volumes.
But, do not make it sound rehearsed or forced. And the best instances where attraction occurs are when you do something to express how you feel without intention.
Remember that a lot of body language is instinctive, and that these non-verbal cues can sometimes speak volumes more than any words you could say. When done right, it can accentuate the tension in your lips, build up the anticipation, and might even lead to sparks flying.