When to Withdraw Your Application
There is no need to withdraw from consideration prior to being selected for an interview. However, once an interview has been scheduled or completed, you should inform the employer if you no longer have an interest in the position and don't plan to proceed with the process.
How to Withdraw with an Email
You can send an email expressing appreciation for the employer's time and consideration, with the option to include a reason such as how the position wasn't a good fit.
Employers may redirect outstanding candidates to other more appropriate opportunities within their organization if they are impressed with the person's background.
How to Withdraw with a Phone Call
If you have established a solid rapport with the hiring manager or Human Resources representative throughout the application process, it is more professional (and considerate) to withdraw from consideration with a phone call.
If possible, speak directly with the hiring manager rather than leaving a voicemail or message. This discussion could lead to referrals for other jobs or even restructuring of a more appropriate position.
No matter how you withdraw from consideration, remember to remain professional and positive. Do not go into detail about why you do not like the company, your potential boss, etc. Instead, emphasize how grateful you are for the opportunity to apply for a position at the company, and for their time and consideration thus far.
A future job opening at the company might be a better fit for you, so you should seek to remain in the hiring manager's good graces.