I've been thinking about this for some time. There are many situations where I arise from a drowsy imagination-ride because I heard something from which I really, really, really can learn. During my schooltime I made huge notes of those things and plastered my boarding-school room with it. At least my half.
This list was never very restricted. It has inspirational quotes, interesting thoughts and ideas for projects... but why just keep that to myself?
Many of these things are open for discussion... So, under the label "the learned" I will collect the things I feel are "insights" now.
1. Support Imagination
If you want to illustrate a story, don't draw what the text says, because the reader is not stupid and has his/her own imagination. Nurrish that imagination, support it. In most cases, illustrations should be the servants of the text it.
Don't draw the strong detective that solves the case - maybe draw the housekeeper finding his carelessly thrown away cigarette buds or the two different shoes he left back, because he was so eager to solve the case. If that fits the character.
(There are tons of exceptions, of course. For instance if you are commissioned to draw an illustration so close to the text that there is no room for speculation left.)