I have a confession to make. One of my least favorite things to do is look for visual references. Be it image-search engines, or taking my own photos - something about the process slows down my creativity and I just plain don't enjoy it.
They say that N.C. Wyeth had an incredible visual memory. Sure, he used plenty of his own references and props, but what made his illustrations so real and palpable were his observations of life. So what I've started doing over the last few years or so is study my surroundings no matter what I'm doing. If I'm walking in the park I'll take note of how sunlight and shadows play on the trunk of a tree, or if in a crowded store, take note of how people interact, or what body language they use if they're standing in groups (drawing group scenes has always been a challenge for me). I'm not memorizing these things - God knows I don't have the greatest memory in the world, but you will find these observations seeping into your drawings--and they will become more life-like. You can't always sketch with a pencil and paper, but you can always sketch with your eyes, right? Try it some time.