As a fan of clean code I like coding guidelines that raise the quality of code by regulating the design and development of code.
Common Design Fundamentals
Probably one of the best known examples is the “Microsoft Application Architecture Guide” that can be found here:
Hint: better use the Pdf or the site map at the bottom of the page instead of the left navigation because it doesn’t show all content. And avoid other languages since the breadcrumb is missing completely.
Here you can find an overview of the key principles:
And here you can find the key principles in detail:
Web Design Fundamentals
Within this guide you find a complete chapter that applies to designing web applications:
SharePoint Design Fundamentals
When you dig deeper you can find guidelines for designing and developing SharePoint applications as well: https://msdn.microsoft.com/en-us/library/ff650022.aspx
obviously the Microsoft patterns & practices page is about to be moved to azurewebsites.net as you can see on the home page: http://pnp.azurewebsites.net/
So don’t be irritated that some content still can be found on the msdn page itself: http://msdn.microsoft.com/en-us/library/ff921345.aspx
(as you can see on the about page: http://pnp.azurewebsites.net/pages/about, section ‘Explore the patterns & practices catalog.’)