The “Mad Men” TV series has given the public a look inside the world of advertising agencies, at least as they (supposedly) existed in the early 1960s.

I worked in ad agencies for 14 years – not in the Madison Avenue shops where they cook up campaigns for Coke and McDonald’s, but at places in Milwaukee, where our clients dealt in industrial products like engines, forklifts and loading dock levelers.

Along the way, I learned a few sayings. Like: Don’t tell my mother I work for an ad agency – she thinks I play piano in a whorehouse. Or: In the ad game, the days are hard, the nights are long, and the work is emotionally demanding – but in the end it’s all worth it because the rewards are shallow, transparent and meaningless.

Of course, I learned other things, too, including the five most critical parts of a direct-mail campaign. You can argue that there are more than five critical parts, or that these are not exactly the five – but there’s no disputing these five are important. The absence of one or more is a reason so many direct-mail campaigns fall flat on their faces.

On the surface, direct mail seems so simple. You don’t have to pay big money for space in a paper or time on TV. You just send an advertisement to a bunch of people. You expect 2, 3, 4 percent to respond. You make the sales and count the money.

Ah, but it’s much more complicated. If you don’t do it right, you won’t get that 2, 3, or 4 percent – maybe not even 1 percent – and you’ll have wasted your money – might as well have just flushed it. If you do the Big Five, you’re not guaranteed success, but your odds are a great deal better. Here they are:

1. List. Doing direct mail without a high-quality mail list is like shooting arrows without a target. You can buy lists from all different sources, so much money per thousand names. But unless you really know the list source, you have no idea how many of the people on it have moved, are dead, or have no interest at all in what you’re selling.

You’ll never generate a perfect list, but you need to be as sure as you can that most of the addresses on it are still valid, and that you’re reaching people who have home sizes, incomes, needs and interests that fit what you plan to offer. Probably the best place to start is your own in-house list of customers and prospects.

2. Offer. What exactly do you want people to buy? And what are you willing to do to get them to buy it? If you send postcards into 20,000 homes just telling people about your expert drain cleaning service, how many will respond? How about none?

But what if you offered them a free drain inspection and a starter supply of a biological drain maintenance formulation as a lead-in to a regular maintenance contract – you know, to “prevent those costly backups that always seem to wait until you expect a houseful of company”? Now you might have given that 2, 3, or 4 percent a compelling reason to respond.

3. Deadline. But will they actually call you? Ask yourself: What do you do with mail? If you’re like most people, you pretty much handle each piece once. You keep it and file it, pay it or whatever – or you toss it. How often do you save things for later? Or if you do, how often do you eventually act on them?

To get people to call, you need to instill some sense of urgency. That means giving them a deadline. “Offer expires at midnight tomorrow.” Or: “Call today for a FREE bonus gift.” Or: “Don’t delay – FREE gift to the first 50 callers.”

4. Package. How you package your offer is incredibly important. You don’t need to send a fancy 3D container or an expensive brochure. You do have to make sure your message hits the recipient right between the eyes.

A plain old postcard will go unnoticed. You need something bright, bold, colorful. An eye-catching visual. A potent headline. Give some thought also to how to address the mailers. Nothing says “ignore me” quite like a slapped-on-crooked, printed address label. On the other hand, a clean business envelope with an address that looks individually typed is just about certain to get opened.

5. Measurement. One virtue of direct mail is that it’s easy to measure the results. You count the number of pieces you sent out and calculate the cost. You count the replies and track the dollar volume of sales that came from them. And you know your return on investment. You also gain intelligence that can guide future direct mail efforts.

That’s certainly not all there is to direct mail, but it’s a foundation. Do you follow the Big Five in your direct-mail campaigns? If so, you’re making the Mad Men proud.