First, let’s start with what “decision making” is, and more importantly – good decision making.
When trying to make a good decision, a person must weight the positives and negatives of each option, and consider all the alternatives.
Clients come with problems. And they want them solved. Most of the time that’s a business problem, not technical. They want growth, they want improvement, they want income. Designing and developing must come with this core idea in mind. You want to provide a product that will improve your client’s business.
But to do so as an agency, you have to understand the business of your client. Why a certain design decision is better than another. What is the user base? How will this design decision affect the technical implementation of it and therefore the budget of your client? Long term commitment is crucial for understanding this.