Smart move to set guardrails before the project starts. This is how you ensure the redesign actually drives growth instead of just looking different. Your instincts are right—the fundamentals are everything. Your list of non-negotiables should be contractual. First, Mobile-First Design & Performance is not optional. Mandate that all page designs are presented for mobile first, with a performance budget (e.g., pages must load in under 3 seconds on a mobile connection). Second, Core User Journey Clarity: Each page must have one primary goal, and the team must be able to articulate it. The homepage's goal isn't to "look impressive," but to "get qualified visitors to click to the pricing page." Third, Accessibility (A11y) Compliance: Require that all designs meet WCAG 2.1 AA standards from the first draft. This means proper color contrast, keyboard navigation, and semantic HTML structure—it’s far harder and more expensive to retrofit later. Fourth, Clear Messaging & Hierarchy: Copy and design must work together. Mandate that headline and value proposition are signed off by someone outside your industry before visual design begins. Finally, build in Validation & Testing from day one. The design process should include plans for A/B testing headlines and CTAs post-launch. For a comprehensive, pre-launch checklist that turns these principles into actionable items for your team and your agency, this article on website design mistakes to avoid is an excellent resource. It covers these pitfalls and provides a concrete "Before You Launch" checklist perfect for a project kickoff.