How should a candidate approach an interview for an internal position as oppose to an external position?
An internal position is a vacant position that is available within the company you are currently working. An external position is outside the company.
Several aspects such as process leading up to the interview, position intel and culture intel would be key differences.
This is from the perspective of a candidate.
The only difference I would expect is that the folks conducting the interview will probably know you (or in a bigger company, know someone in your supervisory chain) - the interview is less of a "getting to know the candidate" event and more of a "Do you have the requisite skills?" / "Can we afford to lose you from where you are?" kind of thing.
Because of this you should expect to be grilled a little more thoroughly on your weak points, and you should have a plan on how you will continue to grow and improve as an employee.
The benefit side of that equation is that when you state some of the projects you've worked on there's a good chance the people interviewing you will be familiar with them. If you've done consistently good work for the company you can expect that other teams will want to have you as an asset.
For the most part, there's no difference at all. You should go into the interview expecting just as much scrutiny as someone who has never worked for the company. However, you should also be prepared to demonstrate how your inside knowledge of the company is an asset, and not just expect the interviewer to assume as much.
I've never interviewed a current employee, but I've interviewed two former employees who left for educational reasons then came back to apply for a higher-level position a few years later. One couldn't remember anything about our products or what she worked on before. The other was able to talk intelligently about his previous work here, and demonstrated ability beyond what was required in his former position. Guess which one we hired?
If you have identified an internal position that you want, your best bet is to get your current manager to advocate on your behalf in support of your candidacy. In most companies I've seen, the first thing hiring managers/HR do with internal applicants is to speak with the employee's current boss.
On that same point, your current boss is going to hear about your application, so he/she might as well hear about it from you. Explain why you are interested, how the new position would help your career development, and how you taking the new job would help the company. Ask your boss for his/her thoughts and to provide a positive reference for you.
I'd probably focus a bit on making sure I have a list of character references within the company to support why I'd be a good fit for the new position. Knowledge of the company isn't likely to be a big focus in the interview though it may be worth knowing what department the new position is, what changes would I be taking and how is this a good move for the company for me to move to there from here.
The reference point here is a bit different since these may be mutual acquaintances unlike the other case where in an external company there may not be that same depth to the business relationship.
