A short letter or email explaining why you have decided not to accept a job is one of the best ways to decline a job offer. Address the letter to the hiring manager who conducted the interview. In the letter, thank the hiring manager for the opportunity to interview for the position but confirm that you have decided not to accept the offer.
In the letter, explain that you're not accepting the position without going into too much detail about the reasons why. Declining a job offer without mentioning specific details allows you to maintain a positive relationship with the company and the hiring manager. In the future, you may find another position within the company that better suits your salary requirements, skill level or current location.
If you prefer, you can also contact the hiring manager by phone to decline the offer. If the hiring manager asks why you're declining the offer, be honest, but try to remain positive about your experiences with the company. As you may meet the same hiring managers again later in your career when interviewing for positions with different companies, it is best to remain professional and polite, even if you didn't like the salary offered or agree with specific company policies.