The value of this may depend on what you are doing, but is a good tip.
1) Susan's example is a great example of my first thought; there is a PDF version of the form that will accept entry http://www.irs.gov/pub/irs-pdf/fw9.pdf. So if you need to fill out a standard form, check to see if there is already and electronic version available.
2) Print to the original form. Once you have your information typed, remove the image from the header and print on the original form. You may want to print on blank paper and check the alignment first, before printing on the form.
3) Scan just the printed area of the form, to allow margins for alignment.
4) If the document is meant to be typed, it will likely expect 10 or 12 pitch and single line spacing.