Depends on a lot of factors. What do you want to study in grad school? Are you looking at MS/A or PhD programs? What are the typical scores of previously admitted students? How do you usually fare on standardized tests?
If you're looking into humanities/liberal arts programs, they'll want high verbal scores and might not give two shits about your quantitative score. Sciences usually like high quantitative scores with solid verbal scores. MS/A programs usually don't demand scores as high as those of PhD programs.
Keep in mind that high scores on the GRE won't get you admitted to a program, but low scores will get you rejected. That is, a good GPA, a good undergraduate program from a good school, good letters of recommendation, and relevant experience (like undergraduate research in the sciences) usually count for a hell of a lot more than the GRE. If you went to a less rigorous school, high GRE scores can illustrate that you made the best of your opportunities. But low GRE scores can indicate that while you might work hard for good grades, you simply won't cut it at the graduate level.
And unless you're considering huge programs that will treat you as a completely faceless applicant, I can't overemphasize the impression an impressive personal visit can make.