Concieve of and work on your own projects. Make things that use software. Scratch your own itches. Eat your own dogfood. Make things. Make things. Make things.

Concieve of and work on your own projects. Make things that use software. Scratch your own itches. Eat your own dogfood. Make things. Make things. Make things. Not just pieces of things, the full things! Don't get trapped in over-specialization, always be able to make things completely. Whatever notion of "full-stack" you have right now, you have no idea how big the stack really is until you try to own it and make things on your own. Also, and this is a big one, to be a truly great developer, you need to transcend "developer" and understand and master the context in which "developer" exists. Let's call that "growing your stack". You will be a much more insightful developer when you see all the moving parts, of which development is just one.