Most of us fill our conversations with a lot of filler. Whether it's "ums", "ahs" or "like", it's one of those things that makes our speech a little harder to follow. Productivity blog Lifehack recommends you keep track of that stammering to help get rid of them.
The occasional "um" is common, and we all do it to buy time while we think of something to say. You don't really need to fill that space with sound, and a couple seconds of silence while you think of something to say isn't going to hurt the conversation. A prolonged "um" might though. To get rid of it, Lifehack recommends tracking every time you say it:
One way of actively paying attention and correcting your habit, is by wearing an elastic band around your wrist during your leisure time. Whenever you catch yourself on saying "um", simply shift the elastic band to your other wrist. This practice trains your mind to notice your use of "um" and eventually omit it.
Powerboost Your Speech With One Simple Trick [Lifehack]