This is really a important part of an interview. Negotiating a fair and practical salary is a critical step in the job search process, and one that can be navigated smoothly if you know what to do and what not to do. Just beware of common mistakes.Sometimes it becomes a reason for you to not accepting the job and also for the recruiter to not give you the job.

Some important points to consider:
  You should know the desired salary range. research typical salaries people are getting for same skill set, industry and experience. Consult your friends and seniors about the salaries.
  Know about the company. If you have any friend or relative in the company , then ask him the general salary range the company provides. Search in Internet/networking sites if the company is good payer or not, accordingly you should go for the range.
  Don't agree on the salary which is too less to fulfill your needs of a good life.
  Try not to give any number if asked for any salary expectations. If the interviewer pressurize, then you should answer like "As per company standards " or "I will consider reasonable offer". If pressed for a number, give a range rather than a specific. The bottom of your range should be the minimum you must make, with the top being a bit higher than your ideal.
  Make sure that you look into company benefits also. Pay good attention to company's medical and dental plan, vacation package, retirement benefits, and other perks.If the company cannot meet your salary requirements, it may be able to make it up to you in other ways, such as stock options or additional vacation time.
  The bottom line is that salary negotiations, like anything else, need to be done respectfully and kept in perspective. But if you do your research, set your boundaries, and always know how to handle the tough questions, chances are you will end up with an offer that works for you and the company.
  Delay salary and benefit negotiations for as long as possible in the interview process. You'll have more power to negotiate when the field of candidates has been reduced to just you - when the employer is completely sold on you as the best candidate for the position.
  Never stop selling yourself throughout the negotiation process. Keep reminding the employer of the impact you will make, the problems you will solve, the revenue you will generate. And continue expressing interest and enthusiasm for the job and the company.