This article by Jeff Patton explains two easy ways to successfully develop software. So simple you can't fail.

Two secrets to success in software development are:

1. Start sooner

2. Build less software

This is sadly simple advice.

Agile development does try to short-circuit elongated research and design phases in favor of beginning sooner and continuing active research and design throughout the development cycle.

12 Best Practices for UX in an Agile Environment - Part 2.

Unfortunately reality doesn't usually allow for this well maybe point number two.