I read about this technique in, I think, Mental Floss- Early in the morning, when you are at your most creative, write down anything that comes to you. This free-writing style is great because you don't feel the need to try and write the world's best novel or whatever and it's strange how things will go. Another thing along these lines is to make a squiggle and make a picture with it.
Other than that, I keep questioning myself to get answers on things I'm thinking of. Here's an example, using my
twin succubi Alla and Valla. I had an idea to sketch pictures of succubi as different RPG class/archetypes. I immediately knew I had to have a priest/ white mage and a typical wizard/ sorceress. I decided to use the upwards chevron /\ and downwards chevron \/ as a feature of them both. Because they were both based off of the same shape, but opposite I determined they were twin sisters. To give a ying/yang feel their hair would be opposite colors, which I justified by saying that the primal forces of positive and negative energy shaped them- which also gave me reason for the red/blue eyes.
Creative people and geniuses have a better advantage because they are able to make connections that the rest of the population can't automatically make. There's been times when people were baffled and I was like "What if it was in reverse?" and it helped. Little things can make all the difference, hence the journal/squiggle exercise. Just let loose and have fun and most importantly write down your good ideas!!!
