Like anything else, too much flirting is too much of a good thing and can make you appear desperate. The key to flirting with someone you are attracted to is to be aware of the timing, frequency, duration, location and response.
Avoid flirting in places where it is not appropriate, such as at work during office hours. When you do flirt, do so in a private place, without distraction and without being obvious. Flirting in a way that is not desperate is not obvious and can include a gentle, brief touch of the arm, a friendly smile or a genuine compliment.