You just have to manage to have the conversation flow naturally. Start by a remark on something, say, the traffic you had to get through to get there, that alone will open the window to rant on something else. And that will as well. And etc.
Preparing something in advance is a sure way to just forget it anyway and screw up even more.
It's probably not the answer you want to hear, but I think each person should ASK QUESTIONS to the other person about themselves. So often, people become nervous and just sit and talk about themselves and it always seems self-centred. Asking about a person's background, family, plans for the future - all get the other person to not only give you information about them so that *you* know they're a good fit in your life, but it also lets the person know, "gee they really care and want to know more about me". Most people love the feeling that someone is interested in them.
Both your interests, what's he interested in? Hobbies, old stories that may be funny, topics that introduce new things about you or him. You gotta get to know him to have better convos with each other.