There's lots of factors to consider, but the best strategy is to keep a list of significant things you have done for the employer that may stand out from what others have done. Especially keep track of particular praises for good performance. Bring these up when you are brought in for periodic evaluations. That's the best time to push for more money. The argument is simple....if you are outperforming your peers, you should be better compensated.
I quit a job not because I was given a small raise, but rather, I was given the same raise as people they just admitted were so bad they wish they could fire them (they were desperate for manpower). If I was not worth more to them than someone they wanted to fire, that seemed to say a lot about what they really thought of me. Incidentally, they tended to lose most of the smart and hard working people over time.
The sad reality, though, is that most people get more money and better benefits by leaving jobs anywhere after 6 months to 2 years because a move to a new employer brings more reward than waiting for it to come in-house. This only reinforces an employer not giving more because if you can be easily replaced, he figures you'll just leave if you can get a better deal. This works against those of us who find applying for jobs stressful.