Print design, like a lot of marketing media, goes through a process which is done to determine the likelihood of success of a piece of design or media. This can be done through the designer’s own experience, or by creating a focus group to judge the work impartially. What is important though is that as much consideration as is possible needs to go into the production of any campaign, so that you have the highest likelihood of getting positive results.
In print design, they will typically design any graphical design around a brand. This allows you to use the campaign for brand awareness as well as for developing interest in products. Maximising impact is the goal. This has several implications; do you focus upon the products, or brand awareness? Usually there is room for both, but in certain instances you need to make a choice.