If you are lucky enough to get a final job interview, you will be presented with one final obstacle: The salary negotiation.
Negotiating salary is a difficult task. Job seekers have to balance what they want with what they need, as well as keeping in mind what the employer can reasonably offer. That's why you should go into the interview with three numbers: What you want, what is acceptable, and what is a non-starter.
The first number you come up with is one that you would make you ecstatic. It's a salary that is beyond what you would expect, but is not so far-fetched to be a complete fantasy. This is where research comes in. You must have a solid understanding of what the average salary is for the job for which you are applying. If you see there are some organizations that are paying their employees on the high-end of the spectrum, you should use it for your "dream salary."
The second number is one that you would accept, even if it isn't everything you would want. This is generally the salary that the majority of people working the job would get paid. For example, The NonProfit Times' 2011 Nonprofit Salary and Benefits Report shows that nonprofits paid their non-management development employees an average salary of $36,817. That would be a salary that would at least pass the "sniff test," and could be a basis for your negotiation.
The last number doesn't require as much explanation. This is a salary that, if you were offered, you would reject without hesitation. This would be something like being offered a $25,000 salary for a job that normally pays in the high 30s. You probably won't run into this situation very often, but it's good to be prepared.
Having these three numbers will help you have a basis for which you can evaluate the offer you are given by the employer. You can then begin your negotiations on a much stronger ground, and that's half the battle.