All forms of marketing have a common theme in order to be successful, and that theme is research. Every aspect of marketing requires extensive research if you want to be successful.
Of course, you don't have to research in order to have marketing. You can ignore researching what your customers actually want. You can choose to ignore trying to find out what kinds of things will best appeal to them, which forms of marketing will work best, and what your advertisements need to say in order to encourage them to buy something. You can certainly do all of that, but you won't end up with any kind of successful marketing if you do.
The fact that you need to research your customers in order to best appeal to them before you print posters or brochures is a better known aspect of marketing. I think that most companies are aware of the fact that this is vital to marketing success.
Instead what happens is companies don't think about how much they should research when it comes to developing the best and most cost effective form of marketing.
Unless you plan on handling every part of your marketing yourself you're likely to have someone who is designing your ads, maybe another person writing them, and of course a printing company who is going to actually get your ads printed off.
Each of these require a lot of extensive research as well if you want to be sure that you end up with not only the best kind of advertisement, but also the best prices.
Let's look at an example of posters. Now, with color posters you're certainly going to need a good graphic designer to get you the best kind of design work possible. I would do a lot of research into the best people for the job before committing to anything.
The printing is going to be just as important. A lot of companies might shop around to find the best poster printing quotes, and that's a good first step, but I'd research more about the printing process than just how much it's going to cost. Different types of printing can not only greatly affect the costs, but the types of paper and ink you use can also affect the way the poster looks.
If you've done your research than you'll have a better understanding of what goes into the printing, and so you'll know what to ask about. Get your poster printing quotes as well, but also ask them about the type of paper and ink that will work best for your poster to get the most polished end product possible.
Advertising is a very large part of what keeps a company going, and so why would you entrust it to people you don't know every much about. Do your research into the best companies to handle your advertising needs, and you'll end up saving both time and money in the long run.