Give a Compliment (or Two)
When it comes to showing interest, sincere praise of either physical attributes or personal qualities goes a long way. Pick a trait that attracts you to the other person, and give a specific compliment about it. If you like his style, for example, let him know how fantastic that jacket looks on him; or, if you're into his mental prowess, tell him how much you admire his intellect. Avoid being too general--it's all about making the other person feel special.
Remember the Details
Recall details of earlier encounters and conversations. Although it's not necessary (and might come across as obsessive) to regurgitate every word verbatim, remembering such facts as pets' names or a favorite vacation spot signifies the impression the other person is making on you and that this information is important to you.
Make a Joke
Humor is one of the best tools at your disposal when it comes to helping you and the other person feel more comfortable. According to WebMD.com, laughter reduces stress and relaxes the body, which in turn helps you relax and open up. Also, if you run across an awkward moment, a joke can be a welcome distraction.
Touches ranging from subtle (a playful punch on the arm) to bold (an embrace or kiss) send can't-miss-it signals that demonstrate your romantic interest. Be aware of boundaries. Start slowly at first, and gradually become more daring. If the contact you initiate is not being reciprocated, it's time to back off.
Click Away for Your Next Date
Don't underestimate the importance of digital media. A quick text, email or wall post can let the other person feel appreciated throughout the work day. Just don't overdo it--you want to avoid looking desperate or unable to interact in person. Keep it simple and light.