Bad answer:

In my last job I earned $35,000, so, now I am looking for $40,000.

If you can avoid it, do not give an exact number. The first person to name a price in a salary negotiation loses. Instead, re-iterate your commitment to the job itself. If you have to, give a broad range based on research you have conducted on that particular role, in your particular city.

Good answer:

I am more interested in the role itself than the pay. That said, I would expect to be paid the appropriate range for this role, based on my five years of experience. I also think a fair salary would bear in mind the high cost of living here in large cities.