That's something I've been asking myself for quite some time, too.
My greatest source for creativity is 'consuming' really good and unique art like the band Daughters for example or paintings from Beksinski. There are infinite great artist all over the world and it is worth your time looking into something beyond your own region or the US.
I think the creative state is something close to sleeping. You probably know that feeling when you wake up after a very vivid dream, remembering it entirely and you think: 'this would make a crazy good film.'. That's why Salvador Dali used to stay awake for a long time until he got sleepy as hell, sit in front of a table with a piece of paper and a pen and then try to fall asleep while sitting, holding a spoon in his hand. When he fell asleep, the spoon would fall to the ground and wake him up by the sound. He then quickly scribbled down what he saw in his dreamy state. I basically do a similar thing, whenever I need an idea for music. I just lay down in my bed or wherever I am and wait...
After my entire life of doing creative stuff on a daily basis, I found that creative ideas are not really created by the artist but rather taken and used. Whenever huge hypes come up in society like triangles throughout the entire 2010s, it is never the case that a single person comes up with it and every body else just copies it from that creator, like often stated by critical people. It usually happens that many people have the same idea and start doing it before even knowing someone else is about to release the same thing. That is because ideas are not created by people, they are already there, we just take them. The word 'creativity' doesn't really fit for what is tried to describe with it. I know it's a hard pill to swallow but once we detach us from that egoistic point of view that our creative ideas belong to us and we are like a godly creator in that way, we are ready to reach into the unknown territory and take those ideas at will.
... So I wait for the ideas to get zapped into my head, not trying to think of anything particular. It always works.
I am currently reading a book by the director Andrej Tarkowski, called 'Sculpting in Time' which is like a revelation to me right now. It is the first time I ever experience someone being able to describe art for what it really is, detached from political statements and moral values or from technical aspects of craftsmanship. This book catapulted me like five steps further as an artist within it's first chapter. I recommend Sculpting in Time to anyone who is trying to develop as an artist.