The first and important thing to consider and to know is how much you are worth. In going for other jobs and opportunities, the salary is usually unknown, but with some research on your part prior to the interview, you can have a general idea of the range and if the opportunity is worth pursuing.
You can tap into the information provided by online sites to give you a range of salary for the position you are going for. Some websites also dig a little deeper and gather salary information directly relating to the job position. By doing your homework, you will go into the interview armed with the knowledge of the range of salary so that you won't waste your time pursuing a sales job opportunity that pays below what you are doing now or is not within the range you are looking for.
Another research strategy to take is to search for your own current sales position and company to see if you are within range to ask for a raise or set expectations for your next sales job search. Career focused forums or connections on linkedin.com can also give you insight on the salary range, if you are comfortable asking, you might connect and ask a current person within the company, "I am interested in the "job here", and was researching about the salary range and was wondering if you would help me understand what I might expect from taking a position with your company". Some people are uncomfortable giving this out, but some will give you the range. You can also ask the hiring sales manager about the salary during the interview, but be sure to time this during the right time during the interview process.
Some online sites will give you salary ranges like salary.com or payscale.com. I also suggest using glassdoor.com or careerbliss.com, which lists positions and salary by company. Another great resource that gives a broad salary range and title is from the U.S. Bureau of Labor Statistics.
Knowing what your worth going into the sales interview will help you negotiate when its time for the discussion of salary. You will also want to consider the salary versus commission mix, pension, 401K match, car allowance, sign-on bonus, tuition reimbursement and paid vacation as part of the compensation package. Do your homework, know what you are worth and what the sales job opportunity is paying and go in with the knowledge to get the salary and compensation you are looking for.