The headline is a summation of what George Lois, considered one of the greatest art directors and 'the original mad man', had to say about ideas.
"I don’t think I create anything. I’m really serious — I discover the ideas.
If you understand how to think… If you have a background of graphic art, and you are a sports fan, and you’re literate, and you’re interested in politics, and you love opera, and ballet’s not bad either, and if you understand people… and you understand language, and you understand that product, and you understand the competitive products… and you put that all together in about ten minutes — the idea’s there."
Be open to experiences and you are likely to come up with interesting ideas. Learn it from masters like George Lois.