Prepare a topic in advance, correct your partner at the end of the conversation, be sure that you and your partner have the same level at the languages you are practicing.

I like to schedule "conversational lessons". Meaning me and my partner arrange like an hour for conversation: the first 30 minutes we talk only in his/her native language, the next half hour we do it on mine.

That kind of focus really speed things up. 

I try to keep my exchanges organised and not too apart. Once per week at minimum.

It is also important to set realistic goals from the beginning and stick to them. I don't mind chit chat but there must be a learning plan which both partners follow.