In an internal interview, the most common mistake people make lies in not saying enough.
So many people go into an internal interview feeling that the interviewer already knows them, so they think they shouldn't or don't need to provide a lot of detail about their skills and experience.
It can feel a bit awkward describing your skills, experience and accomplishments to a colleague who knows you and who may have worked along side you on some of the projects you are describing. It is, however, crucial to provide the same level of detail in an internal job interview as you would provide in any other job interview.
The interviewer wants to hear about your relevant skills, experience and accomplishments. You can count on the fact that others who are also competing for the job will be highlighting all of their marketable skills and accomplishments. So, if you fail to promote yourself effectively in an internal job interview, you will not compare well against the competition.
Although the interviewer is your colleague, he or she may not be fully aware of all of your contributions to the company. The interviewer may have forgotten about some of your major accomplishments, or he or she may not know about some skills you have that you may not use in your current role but would be valuable in the new job.
Some interviewers use a points system to rate interviewees. Before the interview, they will determine several key ideas they are looking for in the answers to each question. When you mention one of those key ideas in your answer to an interview question, you get a point. If you fail to provide details in an internal interview, you will not perform well in a points based interview.
For example, you may know the four steps required to perform a specific task that the interviewer asks about, but if your answer only details two steps because you assume that the interviewer knows that you know all of the steps, you will only get two points for your answer.
Handle internal interviews in the same way you would handle any other
job interview:
the way you would for a job interview. That means on the day of your interview, you should be dressed better than you would on a typical work day.
Get across the idea that you have and will continue to bring value to the company without being negative about your colleagues.