The generally accepted format for numbers in prose differs from technical writing. Most of the time, technical documentation will deal with a larger volume of numbers, especially measurements and statistical data. When writing a large volume of numbers in this instance, stick with using the Arabic numerals. It keeps the numbers in context, and is easier to compare data and conclusions.
When it comes to prose, the rules change. Most of the time, the numbers will not be grouped for statistical or measurement purposes, but instead be presented as a part of a description or timeline. If one is able to express the number in two words or less (one, twenty-five, eighty-seven), spell them out. Use hyphens between the compound numbers, or if they happen to be part of a description, such as four-pronged attack. If a sentence starts with a number, spell it out or consider revising it.
Of course, there are exceptions to the rules. If you are expressing multiple numbers, use the same format to make it easier to compare. For example, one would say Four out of fifty dentists recommend Bob's Hogback Chews for their patients who chew disgusting things, instead of Four out of 50. In the same vein, one should express symbols in the same manner, such as $10 or ten dollars, not ten $.
When using numbers in dates, stick with the written-out form of the numbers if they can be written in two words, but numbers when they cannot. "Your sixty-five page essay is due on August the twenty-fifth."
There are two generally accepted methods of expressing a full date: the American (month, day, year) versus the universal European format (day, month, year). In all honesty, the European method makes more sense, building up from smallest unit to largest unit of time. Use the numbers instead of writing them if you use one of the standard formats: July 28, 2007 or 28 July 2007. To avoid mixing up the dates when your audience includes multiple continents, avoid using all numbers, such as 10/4/2008. Is it April tenth, or is it October the fourth?