You can’t be prepared for every salary interview question
You can't be prepared for everything, but you can be ready for most eventualities. The steps to getting prepared are pretty obvious. You have probably have thought of all of them. Still, I find it's helpful to put all my salary considerations down on paper and then review them before going into an interview. 
1, How much do you want to earn? Realistically, how much do you think someone with your skills and experience should be able to command? People with several years of experience in a field have a pretty accurate sense of what the market will bear. But if you're new to a field it's a bit more difficult. Do some research. Talk with knowledgeable people, check with an employment recruiter, search the job information that's so plentiful on the Internet. And remember that salary is only one part of the compensation package. An employer may offer other benefits that reduce your salary requirements. Health insurance, a retirement plan, profit sharing are all worth money. In your research, try to find out how quickly compensation increases in your line of work. How much does someone with, say, five years of experience typically make? Future year earnings potential may alter your views of how much you need to make initially.
2, How valuable are the non-salary benefits to you? It's not enough to know what they are. You should put a price on them. If, for example, you really need health insurance, then the value of that policy to you would be equal to what you'd have to spend if you went out and bought your own. You should know how much lower a salary you could accept or how much higher it would have to be, depending on whether or not the job includes a good health insurance program. Suppose you don't need health insurance. Then you should estimate how much money you'd be saving the new employer who didn't have to provide it to you. If it's offered as part of the package, say you'd rather take an increase in salary instead. Perhaps your employer offers commuter subsidies, day care facilities, or other perks that offset your costs of going to work. You should determine what value you place on them and factor them into the salary that's offered.
3, How low will you go? At some point, the compensation just doesn't justify getting dressed to go to work in the morning not unless you're independently wealthy and only work for the fun or it. Or unless you're willing to moonlight doing pizza delivery. You need to know when you walk into an interview what your absolute bottom line is, including the trade-offs between salary and other benefits you might be offered. That doesn't mean you should tell the interviewer what your bottom line is, since your floor could become the interviewer's first point of negotiations. But you should know what it is.
