If you like him then I would start by smiling at him. Then ask him how he likes the company you work for and let a conversation flow. Think of some other questions like what are your hobbies, what kind of music do you like etc..It is always hardest when you like someone to know how what to say but once the ice is broken it gets easier...Good Luck!
Sounds like he likes you. Do you like him? Just relax and take it easy things always work out the way they are ment to...sooner or later. Good luck and the very best of wishes.