Investigate the salary range at the company for your position ahead of time. If you can, look it up for specifically for your city. You should know that going into the interviews. After all, if the pay's too low, then the interview could be a waste of time.
If you give the interviewer you current/past pay information, make sure that you include any possible bonuses with your number.
FOCUS ON NAILING THE INTERVIEW. Managers are usually willing to concede a little more to make sure that they get the person who they want.
If the first offer isn't enough, then tell the manager that you're really interested in the position, that you want to join the team and you want to know if he/she is negotiable on the pay. If the answer is "no," then maybe you can negotiate additional benefits, such as time off. If the answer is still "no," then you have to make a decision.