A lot of options you see when you launch a scanning utility are best left until you have the image in photoshop where you have a wide range of powerful image correction tools.

Apart from choosing the appropriate resolution and mode before doing the final scan, it is essential to ensure that you are obtaining all of the information the scanner is capable of acquiring.

Once detail in an image is lost corrections to those areas cannot be performed in photoshop - you need some tonal information present! The aim is to keep all doors wide open at this early stage of the imaging process.

This is really most evident in the highlights and shadows. Look at your original and compare it to your preview scan. Is all of the detail in the original visible? If the highlights have turned white or the shadows have turned to black you will need to ask the scanning utility to remap  the tonal range to attempt to improve it.

Every scanning utility is different but most have black and white point eye droppers which you can use to set the lightest and darkest points in an image. The aim is to sample the darkest part of an image that contains detail as the black point and similarly with the white point. The scanner will then usually rescan and remap the tonal range in accordance to the points you've selected.

The aim here is to make sure that the scan is the best that the scanner can do with regards to the tonal range. Every other flaw can be corrected better in photoshop, but if you blow the tonal range too badly now, life is going to be pretty bad from this point on!

Remember, you want to optimize the tonal range, but don't confuse this with the scanning resolution!

You can fine tune everything once you get into photoshop!!