The number one key to cultivating ideas is minimizing distractions.
Did you ever notice that some of your best ideas show up when you're in the shower? It's because your mind has nothing to distract it.
When you're going from one place to another, turn off your MP3 player or car stereo (if you're walking / driving). Put your phone on airplane mode so you're not interrupted by texts and calls.
When you're at home, do one thing at a time. If you're doing the dishes, just do the dishes. If you're talking with other people, just talk, don't put on the TV in the background, turn off the radio.
Cultivate as much stimulus as possible overall - but do it one at a time. You should watch the movies you like, read that books you find exciting, explore just to explore. But you also have to take time to focus and just be.
The other important thing is to always have something to write on. Get yourself a tiny notebook that can fit in a jeans pocket, and even a golf pencil if it means you'll always carry it around. No idea is too small to jot down - they all add up.