Experience will of course be one of the biggest determinants of final pay. A designer that has been exposed to the demands and requirements of a lot of different assignments is likely to have a broader perspective and understanding thereby attracting higher pay. That said, it is important to note that experience may not necessarily be in terms of number of years spent in the industry but rather the variety of task types one has been exposed to.
Another factor that will play a part in overall pay is the level of specialization of the graphic designer. Just like many other jobs, graphic design ones are not homogenous. There are certain forms of graphic design that require highly specialized skills. The principle of cause and effect means that this level of skill and specialization will attract higher pay. An example of this variance in pay can be seen by looking at graphic design jobs in the advertising industry versus jobs in the print media. Designers working in advertising companies will often be paid more because of the wider variance of the types of demands between projects. Each client will have his own expectations and the advertising company must have staff that has the skill to adapt to this dynamic environment. On the other hand, designers in the print media may have a routine role and this implies that on average, their level of compensation will be lower.
Then there are the extraneous factors such as location. Pay can vary based on where the job is based both in absolute terms and relative to the original home area of the designer (for a graphic designer that may be required to relocate to a different city, state or even country). Variance on salary at two different locations is also driven by the cost of living. Thus, a graphic designer that works in Geneva, Switzerland would earn more than one working in Mumbai, India though their scope of work and responsibilities may be identical.
One of the reasons why graphic design is popular is the ability to freelance. This is a career where you can actually earn a living without ever stepping out of your own home. The difference in pay between freelance and employed graphic designer is not that clearly defined. At some point, freelance designers will earn more than employed designers. In other situations, employed designers would earn more per hour that their freelancing counterparts. The reasons for these are different; from the ability of the freelancer to cut off the design company as the link to the client, to the ability of design firms to lock in on larger contracts and therefore pay their staff better.
All these are factors you must keep note of when negotiating pay and as means of managing your expectations as you embark on the journey towards your graphic design career.