The words are the most important part of your sales and marketing communications.
Until the words are well developed and begin to focus on the proposition, any design work will be carried out in a vacuum.
A lot of very attractive work might be done, but creativity will be leading the communication.
By adopting a words first approach, you will be able to judge how well the copy reflects the brief.
If the words are right, then the concept is usually sitting there in the first few paragraphs, just waiting to be exploited by the designer.
With well-defined messages in the text, everyone can exercise a degree of objectivity in judging:
How well the images support your messages
If the design allows information to be retrieved from the web or printed page in the right sequence and with the right emphasis.