An old wife's tale has it that the reason we use umms, and ahhs, and you-knows it because we haven't quite thought through exactly what we want to say. The same tale says that's the same reason that people use curse words, because they haven't stopped long enough to think about and formulate what they REALLY want to say.
So, in place of that you get the, you-know, ummmm and so on. Know what I mean?
Well, this is one of the easiest things to conquer when you're recording because not only can you easily edit out those ugly monsters, you can prevent them from occurring in the first place by using a prepared script - either in the form of an exact script or an outline.
If you've taken the time to formulate a thorough script of what you plan to say, you're less likely to have a reason to throw in a filler like You-Know, because YOU really DO know what you want to say.
Besides planning a good script, the next thing you want to do is to read it aloud to yourself - several times. Don't worry about sounding silly. Just try it. Because it works!
The reason it works is because it prepares you for "what's coming next" when you're reading your script. Sure, it's a bit of a hassle. But I'm sure you'll agree that re-recording a track fouled by umm's and ahh's takes a lot more time and effort than doing it right in the first place!