Let me tell you—this will KILL and I mean—RUIN your chances for a follow up interview, especially if your first interview is a phone interview. 

As the interviewer on a phone interview, I have nothing else to focus on other than the sound of your voice.  If that sound is constantly interrupted by an umm, or a ya know, I’m really going to notice it.  If the job I’m considering hiring you for has a lot of phone work involved, I’m not going to subject the person on the other end of the phone to your poor verbal abilities.  At this point, I don’t care if you are the most qualified person on paper—you’re out of the running because your message is being lost in a sea of these verbal crutches.  It’s a very silly way to get eliminated. 

Here’s how you clean up your act.  First, you need to either ask your friends very seriously and honestly if you are a verbal crutch offender.  Explain to them how important this is in your job search, and unless they want to hear you whine for an additional six months about not finding a new job—they should help you.  Verbal crutches are bad habits that can become more apparent when you’re in stressful situations like job interviews, but are probably apparent when your guard is down like when you’re hanging out with friends.  They don’t just appear when you pick up the phone for an interview. 

Your other option is to record yourself while you practice for the interview.  This can be trickier because you will of course know that you’re taping and will make more of an effort to clean up your act, but it could work. 

Another option is to just make a conscious effort throughout the day to listen to what you are really saying.  Too many times I find that if I’m not completely engaged in what I’m saying and am not truly “in the moment” that I will start umming and ahhing as my brain searches for the next coherent thought.  When I focus on the message I’m trying to convey, my speech patterns clean up immediately and I’m back on track.  I sound more professional and people have a tendency to not tune me out because they’re tired of trying to sort out the wheat from the umm and ahh chaff.  

So bottom line, if this could be a problem for you—fix it NOW!  Make an effort everytime you say something during the day to really listen to what you are saying—don’t tune out!  If you want the interviewer to pay attention to you—you need to pay attention to you. For some people, this will be a hard habit to break, but it is well worth the effort, I guarantee it.