The first suggestion author Michael J. Gelb makes is to start a journal. Da Vinci kept journals. He noted down everything from words to animals to plants to… Anything he was interested in. He wrote down new-to-him words and their definitions. His journals include drawings. Basically, it was a way for him to reinforce what he was learning and to be able to look at it later. It was also a good way to keep from losing ideas.
The second suggestion Gelb makes is to write down 100 questions that are important to you. This should be done quickly and in one sitting. Don’t worry about spelling or grammar -- just get the questions down. He has some other exercises that work around these 100 questions, so it is important to do the exercise correctly. Themes may develop. You may see what questions get asked more than once and what subjects occupy your mind.
I have included my 100 questions below. But write yours down first. You might find it illuminating.