Enter a higher print quality setting in the Print quality box (Print dialog, General tab). Keep in mind that selecting a higher setting may slow down your print job. Conversely, selecting a lower setting usually speeds up a print job.
If the colors that print don't match the ones on the screen, make sure the Match Screen Colors check box is selected in the Print dialog box. If this check box is dimmed, your printer or monitor may not support Image Color Matching.
The underlying resolution of your picture may be too low to produce a good print. If you scanned the original picture, try rescanning the picture at a higher resolution and then reprinting it. For more information, see about choosing the right scanning resolution.
Using premium grade paper will significantly enhance the quality of your prints. If you have trouble locating high quality paper, contact your printer manufacturer for suggested sources.
Check your printer to see if it needs a new toner or ink cartridge.