I think most conversations tend to fail when, as Trailer Trish said, it becomes a boring one way conversation with one person making all the effort and the other offering not much more than scant responses. It soon feels like a questionnaire session with the asker (the person taking the lead) feeling tired of having to make all the effort to keep flow and converse. This happens A LOT.
Conversations aren’t difficult or laborious affairs, in his book How to Win Friends and Influence People author Dale Carnegie wrote that one of the best ways to encourage a friendly relationship is to show an interest in the people. Everyone wants to feel like they are special and everyone wants to be heard, those are basic human traits right there, but far too many conversations fall into one person showing all the interest and the other giving nothing in return. Conversations like most things in life are a two-way process and as much as you want someone to be interested in you, you then have to be interested in them in return. This applies to both real life and online.
Throw in a few questions and LISTEN to their answers, ask them about themselves, a common situation or some experience you may share, use that information to take the conversation forward. Sure there are going to be times when you’re expected to just listen, nothing wrong with that at all, but if listening is dominating your role in the conversation (as in you’re always listening but never being listened to) in can get far too tiresome. Like I said it is a two-way process, if one side isn’t making an effort then it will soon fail, it’s just common courtesy.