Observe
Observation is the greatest skill a designer could ever have. Anything you see or do or eat or visit, pay attention to details. Years of psychological studies suggest recognition works better than recall. That means when you observe things around you closely, your brain starts creating patters and you would start co-relating things that you would’t have thought could ever relate to each other.

In terms of graphic design, best inspiration comes from what you see around you. There’s a ton of activity always going on around us and our brain choses to ignore most of that stuff so it can focus on the task on hand. Once you train your brain to grab that information and analyze that, you’d make it more stronger and ‘creative’.