Reading the book Creative Confidence on how to stay creative, written by Tom & David Kelly.
The creative juices comes from life. To be mindful of all the surroundings and engage with the world with in a more proactive way one pumps us with ideas.
One of the ways to do this is to keep a bug list with you. Every time you feel annoyed or notice something that's not satisfying, whether it's a door with a push sign but with pull handles, or bad habits people have like texting while driving, make a note. Instead of complaint, ask yourself the question "how might we improve this?"
I just downloaded an app called Google Keep, where I can quickly write ideas occurred in my head. It helps keeping them in one place and make me more attentive to the things around me. It's a good practice.