Take a look at this article from The Art of Manliness blog. Yes, it’s gender-centric. But the advice is good for anyone, and really is more properly focused toward men. As the article notes, men are much more likely to use filled pauses (ums, uhs, etc.) than women.
So try to look past any perceived bias to the pragmatic explanation of where filled pauses come from and what to do about them. Just read Becoming Well-Spoken: How to Minimize Your Uh’s and Um’s by Brett and Kate McKay (does it help that the co-author is female?).