When reviewing a resume, nobody wants to read over ten pages of information that is crammed into four pages with an 8pt font - in general, nobody wants to read that much information.
It is common for applicants to try and fill up their resumes as much as possible in order to seem more accomplished. However, no employer wants to know that you played field hockey in high school and they most definitely do not want to read an entire essay about it. Be sure to list only things that are of importance and do not elaborate too much - we're not saying you should not be vague, but if they are interested in something, they will contact you.
You should also be careful not to use too small a font. A standard 11pt font is perfect. Be sure to keep it in the normal range. You can use slightly bigger letters for the headings in order to improve the appearance.