Ummm, Ahhhh, You know, this is a tough topic for those who speak.
Many who are nervous or inexperienced about speaking in front of an audience are scared of pauses, and they fill in the gaps with filler words, repeated sayings, grunts and other noises. They often do not know they are doing it, and have no idea how the continuous use of such "verbal tics" can cause the audience to lose track of their message.
If your verbal fillers are too prevalent some members of the audience will begin to count your "ums" and "ahs". I once tallied 65 such tics from a speaker in a thirty minute presentation. Another speaker said "Ya know?" so many times in his talk that I wanted to stand up and scream "YES, I know!". I have no idea what either speaker was there to say to the crowd, but their repeated unwanted sayings were forever burned into my memory.
While these verbal tics are usually seen in inexperienced speakers, I have witnessed highly paid professional speakers and top politicians who also suffer from this unfortunate distraction.
The best way to know if you are making the mistake of overusing "ums" and "ahs" is to ask a friend or co-worker to attend your presentation and to look for the little things (like verbal tics) in your speaking style that are harming the effectiveness of your message. Recording your speech and reviewing it yourself will also make you aware of the bad habits.
Having someone count the number of times you make these noises to fill in your pauses will surprise some people. However, your awareness is the first step to getting past this bad habit.
Do not be scared of a pause in your speech, even if you are searching your mind for the next word. While it may seem like an eternity, often it is only a second or two that you are there without making a sound. While your fears will wrongly make you feel it is awkward, if you learn to hold the silence with confidence, the audience will be drawn in by your powerful use of a pause.
As with all parts of public speaking, your awareness and practice will help you improve your skills.
Have A Great Day.