How to get the best scan ?

• Make sure the scanning glass is clean and free of dust.
• Ensure the document is flat against glass for optimal sharpness.
• Use USB whenever possible for faster scan speeds.
• Ensure scanner settings is correct for image type (e.g. colour or b/w).
• Get the scan right the first time : No amount of Photoshop magic can fix a botched-up scan job.
• Scan at proper resolution for maximizing scanning speeds - you don't have to use the full 1600 dpi quality stated in the specifications because you would need more RAM and it takes up more time in scanning. Speed of scanning is highly dependent on he computer that you are using. See Point 5 for the optimal resolution size.
• Get the colour calibration right : Scanned job look different on the screen of different monitors because of different colour calibration.Use a proper CMS (Kodak's CMS and Apple's ColourSync for monitors) to overcome this niggling problem.

​Source: Canon