Salaries and benefits are a huge expense for most companies, so they have a self-interest in keeping them under control. At a company of any size there is probably a 'salary structure' which defines a range of salaries for employees in specific positions. The structure will say something like an Admin Assistant I can be paid between $20,000 and $27,000 per year, and an Admin Assistant II can be paid between $25,000 and $32,000 per year. There should also be a 'ladder' which defines the differences in skills and responsibilities between an Admin I and Admin II.
So you can see why it's important for you to understand the structure and the ladder. Some companies will make the whole structure public, but in any case it's important for you to understand the range is for your position and the position(s) above you. If you are making $26,000 as an Admin I, it will be difficult if not impossible for you to get more than a $1,000 raise unless you are promoted to Admin II. You'll need to know where on the structure you sit to know how much of a raise you can get.
Obviously, the best way to get a bigger raise is to get promoted into a position which has a higher pay band. At your annual performance review, you and your boss should discuss how your skills and contributions map onto the promotion ladder and what you need to do to get promoted to the next level.
Smaller or less-structured companies may not have a formal ladder and there is more discretion in doling out salaries.