Microsoft has now updated their developer design website with new content for designing UWP apps. You can now learn how to design a Universal Windows Platform (UWP) app that looks fantastic on all Windows 10-based devices, from phones and tablets to PCs and Surface Hub.
- Design basics: Get started designing UWP apps: learn about the platform, UI design fundamentals, and responsive design techniques.
- Design downloads : Jump-start your project with design templates for PowerPoint and Adobe Illustrator.
- Guidelines: Browse the comprehensive list of guidelines for layout, controls, user interactions, text, and more.
Find more about it here.