I do this too. And sometimes I don't realize until afterwards.
Sometimes, if it's someone I see regularly, I'll write a letter and focus on questions I want to ask. Or just a list of questions. I don't have to give the person the letter, but sometimes writing it down helps to remember it. Then I've got a sort of concrete script. I have to stop myself from scripting my own responses to the questions when I do it.
In general just practicing helps. When I notice that I'm running the other person over I try to stop, let them talk, ask questions. Practicing does help for me. But much more so if I find the other person really interesting.
I also try to let the other person know that it's something I feel like I have a problem with, that if I start to get carried away on a monologue they should let me know. That I will appreciate it if they stop me when I'm doing it so it can be a better interaction.
It can be a lot of work, and there are always ups and downs. Sometimes I just completely run the other person over, one day I trapped someone I consider a friend on a corner for 45 minutes with a big long monologue. She was crying! I realized I was doing it and just couldn't stop. I felt terrible about it! I apologized to her a number of times.
Other times I'm trying so hard not to go off on a monologue that I almost don't say anything, I know that if I start talking I probably won't stop.
It's always challenging, one way or another.