Understand what other people are getting paid in similar job roles. This knowledge will give you the confidence to know that you are asking for a reasonable salary. And, chances are, the employer has a pretty good idea of the salary range, too.
Armed with a legitimate target salary, your next challenge is to explain your value to the employer. Use specific achievements from your past in your argument. It is crucial to position your argument well. For example, you don’t just want more money. You deserve more money.