Easiest way to do this is to roughly time how long they spoke for and contribute back the same amount. If you do it right, you'll wind up spending 50% of the conversation talking and 50% listening, which is a reasonable split :)
So I propose the following. Instead of using the simple heuristic of talking half the time which will work with nearly everyone practically always (modulo some edge cases when people have literally no strong opinions about anything), use the wealth of your experience as a human being to establish when and when not to promote complex human social interaction, additionally taking into account contextual and mitigating factors, while simultaneously ensuring that all parties are satisfied with the level and intensity of discourse instead of taking some random Internet person's sound bite advice.