1. Jack stared at her until he was sure he'd caught her eye, then he looked away, glancing back a few short seconds later.
2. Jane leaned forward in her chair, her legs crossed with her hands clasped on her knees so that her arms squeezed her bosom a little.
3. He grinned and raised his eyebrows at her, raising his drink in the same movement.
4. Her lips parted slightly as she slowly returned the smile.
5. That was as good an invitation as any. Jack sauntered over, sitting down on a nearby chair and leaning forward a little in his chair (mimicking). "Hello."
6. Jane tossed her head back, running her fingers through her dark blonde hair (preening) as she rose to her feet. "Hi there."
7. Jack rose as well. "Going somewhere?" Her hooked in his thumbs in his pant pockets, fingers splayed. (A cocky framing device for his, um...)
8. She flicked her gaze from his shoes on upward. "Maybe. Depends."
9. His grin broadened and he cocked his head to one side, waiting. The silence stretched on, so he asked, "On what?"
10. She bit her lip lightly, holding it there for a moment. "You."
11. He chuckled and glanced away from a moment, then turned his attention back on her. Boy, she was making him nervous. "Oh?" His throat was a little dry, so he cleared it, and tried again. "Oh yeah?"
12. "Yeah. Maybe." She shrugged and flicked her hair back over one shoulder.
13. He took a short step closer to partially close the gap. Now they were in touching range and he sure wanted to touch her. Still, this girl wasn't exactly subtle but that didn't mean he was home free yet. (proximity helps)
14. She held his gaze for a few additional minutes then dropped her gaze, almost coyly, to the floor, moistening her lips as she did so.
15. He resisted the urge to touch her, to gently lift that chin and lean forward to kiss her. Instead, he scratched at his chin. "So, uh, can I buy you a drink?"
Okay, this isn't the subtlest of flirtations but I tried to show a range from the arsenal. Remember, though, that flirtation is very particular to the character. Some may flirt simply by talking to you. Others might draw on a wide range of coy behaviors.