Recently, a friend of mine was working on a flyer. She was having a lot of problems with her photos. They didn't look good when they printed out. To get the best scans possible, you need to think about the end result first. For example, she had been scanning them and converting them into CMYK format in Photoshop.
CMYK stands for cyan, magenta, yellow, and black, which is the color model used for commercial printing. However, if you are not sending the images to a commercial printer, you probably don't want to use CMYK. My friend was going to print her flyers out on her inkjet. Most inkjets use the the RGB (red, green, blue) color model. CMYK colors don't print well on an inkjet designed to use RGB.
When you scan, you also need to know the resolution of the inkjet (or whatever printer you plan to use for the final output). Here's why. To print a photo on paper, the printer uses what's called a halftone. A halftone is made up of a series of tiny dots and its resolution is measured in lines per inch (lpi), not dots per inch (dpi) like your printer. (The lpi is often also referred to as the line screen.) Depending on how the printer manufacturer has developed the driver, your halftones probably should be scanned at significantly less than the stated resolution of the printer.
For example, a 300 dpi inkjet tends to print photos at about 60 lpi. You then scan the photos at 1.5-2 times the line screen, so you would want to scan your photo at about 120 dpi, assuming you scan the photo at the size you plan to use (i.e. 100%). Scaling the photo in a desktop publishing or word processing program affects the resolution. If you scale it up, you lower the resolution. The lower the resolution, the more jaggy or fuzzy the photo looks. So to avoid degrading the image, you'd need to scan at a higher dpi. For example, if you plan to scale the photo up to 200%, you'd need to double the scanning resolution, so you'd scan it at 240 dpi.
However, all of these settings vary by the printer. Usually your printer's user guide will say what the best resolution is for scanned photos.