Sometimes interviewers will ask what your salary expectation is early on in the interview. It would be in your best interest not give a dollar figure by diverting the interviewer away from this question and letting them know that it is negotiable later in the interviewing process.
Turn the discussion to the requirements and duties of the job that you are applying for and discuss your attributes to these requirements. Keep the focus on your value and how you can benefit them. Discuss what is expected from you in the open position.
Do not put your pay history on a resume and do not fill in expected pay on an application. Instead enter that the salary is open to discussion during the interview process. If your qualifications are right for the job then you can expect to get an interview for the position.
Many times the interviewer will ask your salary expectation in order to give low ball offers due to the overwhelming response to the job ad. It is a form of disqualification of some of the applicants. You can avoid this by not specifying a salary requirement.
Negotiations for salary should take place later in the interview process and not at the beginning of the interview. Express your interest in the job but let the interviewer know that you would like to discuss the expectations of the job before discussing salary negotiations.
Employers are still looking for the right fit for the job at the best salary negotiation possible. If you are right for the job they will be willing to negotiate the salary at an appropriate time during the interview process. It is up to you to keep that negotiation open during the interview.