Designing a website? Who will use it? What are their needs? What will they be looking for? What will they notice first? What information do you want to convey to them? What do you want them to do? What language will they understand best? What is the optimal navigation path for them?
Writing copy for an email campaign? Who are you writing for? Where are they in the process of interacting with your brand? How do they feel about your brand? What do they need to know now? What will hold their attention? What do you want them to do? What next step do you want them to take?
Creating a television ad? To whom should this ad appeal? What state of mind will they be in when they are watching the ad? How familiar are they with your brand? How will you appeal to their values and their emotions? Do you know what their values are? How do you want them to respond to the ad? What do you want them to feel? What do you want them to do next?
Top marketers naturally think like this - not just once in awhile but all of the time.
If you encounter a "marketer" who seldom considers the customer's perspective, don't hire him or her. If that person is a close friend, suggest that he or she might consider pursuing another career. This insight has to come naturally and it has to be active 24/7.
I have encountered marketers who are good at graphic design or copywriting or social media but do not think in this way. At best they will be good tacticians if given enough direction. But they will never be great marketers.
Do you want to be a great marketer? Think like your customers. Put yourself in their shoes.