In advertising, the best partnerships are usually those formed between art director and writer. The reason for this is in their job titles:
Art directors think visually.
Writers think in terms of narrative.
I begin by looking at all of the packaging ever used by the brand as well as their competitors.
What colors, symbols, and shapes do they use? Why? What does it mean? Etc.
This allows me to get an overview of how the industry has defined itself, and what packaging conventions I could work on to differentiate the brand from its competitors.