Lessons
Get over yourself
Let's say you have to design around something created by the people who use your software, e.g. a photo, a blog post, a page title.
Respect what your users have created
Have they uploaded an image? For god's sake don't crop it to preserve the integrity of your gorgeous grid design. Preserve the integrity of your user's creation above all!
Don't think for too long
Better to make a few prototypes than ruminate on a single one. Better to go with a single prototype and change your mind later. Better to act, immediately.
Learn to code
You will become a more effective design if you understand how to code the software you're working on.