How to keep a conversation with a girl ?

Actually im too bad with that, just too bad. Recently i joined a company for the job and got a light colleague circle there, in the first week i didn't say anything much so the girls kept an image in their mind like im boring, straight forward, over thinker, not frank, not talkative etc but even they're all impressed of my personality, body language, accent and pitch because they always gives a give a good compliment on that. But problem is, now when i try to say something i usually get ignored. I dont know how to talk good and keep convos with a girl and i dont have a good sense of humour even but its not that mean maybe im boring, cuz for my other old friends im just too good. How can i work up on that situation, just help me out!