6. Use action colors. The bright primary colors red, orange, yellow, green, blue offend corporate ad specialists, because they are strident. Which is why they work. (Brown, buff, silver, mustard yellow or beige print colors convey quality, but they do not excite. Do not use them, if you want response.) Paper color in a direct mail letter should be white or cream, with black or blue print, if you want response, as these combinations are the easiest to read.
That said, there's evidence that printing your reply card or other action device on a pastel colored stock, say, green or blue, will lift response, as it calls attention to itself in the package.
7. Every design feature must sell. For example, you'll certainly create attention if the top of your letter is covered in dirty fingerprints printed in a second color! But they had better lead directly into your key benefit. For example, "These aren't the only marks burglars leave behind" - for a security product. "How often has the repairman had his fingers on your photocopier?" - for an office equipment firm.
Graffiti grabs the reader too: hand-scribbled notes, arrows, circles, diagrams...printed in a second color. Yellow highlighting over your key points also lifts response. Underlinings work, particularly if done by hand in a second color.
But because these devices are so powerful, each must reinforce a benefit and be used with discretion. Over-doing them leads to clutter.
8. A direct mail letter should be computer-produced...and should look like an original, just like your office correspondence. Not typeset. Not justified at the right margin, even if your word processor makes this easy. Indent heavily the start of each paragraph. And leave wide margins left and right, at top and bottom, of your text.
9. The more items in a direct mail package, often the more responsive it is...(and the more expensive). Start with a full, busy package: use the response from this as your control. Then take elements out one by one until the profitability falls. This is better than starting with a lean package and building up, because you can test precisely the relative value of each component. And you are less likely to get discouraged by a poor initial response.
One advantage of direct mail is that there is a massive amount of historical data showing what works and what doesn't. It's as much science as art. Put the known science of direct mail to work for you.
For more specific ideas on how to put some of these ideas into practice, check out 10 Direct Mail Ideas to Boost Your Response.