Know the going salary range for the position and your personal financial needs before the interview. The most valuable salary resources are state employment offices, professional associations for your industry, annual salary reports, direct contact with the company or it's competition, and internet career sites. The issue of compensation includes many possibilities besides just salary. These include basic compensation, benefits and perquisites. Basic compensation may include base salary, sales commission, and bonuses.
Benefits are typically vacation time, sick days, personal days, and insurance.
Perks are all those little extras you will want to consider negotiating for. You should also consider the various types of basic compensation available, especially if you are in sales. Once you know what you want and what is realistic for your position level, you still have to have an offer before you can negotiate. The employer most likely will not make his or her first offer at the top of their range. If you have done your research and know that this type of position typically pays higher, then you will want to negotiate.