That's a pretty abstract question. Conversation can be about anything and each conversation is unique with each person, so I can't really help you. But look at some canned material, personally I am a big fan of improv it requires a quick mind but that is ok.

So here is my suggestion, take out a note book and start doing a bit of roleplaying. Think of it this way, you are a playwright and you need to write a romantic/funny script between the main actor and the actress, create things for you the actor to say and possible responses. Then like any actor on stage memorize this conversation by heart, make 5 "scripts" more just like this. And these will be your conversation topics from now on until you get better.