This is the question so many people will struggle with! All I ever do is casually say, work it into something. First find something you both like doing like...going to the movies or playing baseball, just SOMETHING. Slide it into the question. Example:
"Yea, I was playing baseball with my brothers the other day! We could always use another player, what's your number so I can give you call for the next game!"
Work it in along those lines, it seems to work well and because your saying it with something you both like to do it comes out as normal as ever. Good luck!