The best advice I ever got, and actually followed, was to keep sketchbooks. I have different sketchbooks for different projects. I pick them up all the time to see what I was doing, if I can use something I overlooked, if I have something new to add. I don't mean sketches of Michelangelo's Pietá necessarily, I make children's books, so it's probably a frog and an alligator in a camper van! Start filling sketchbooks! There, I told you! Ideas can be forgotten, commit them to paper.
All I ever wanted to do was draw. When I was very young I would copy the characters from the Beano comics I read. As I got older I drew portraits, sometimes copying historical figures from my school history books. I daydreamed of the freedom to draw all the day, I hadn't considered that it would qualify as a "job". As i mentioned, drawing characters is my favourite thing. That's how i came to make children's books; these characters needed a story in which to play their part.
i remember fondly all the hours I spent in my room drawing. Thinking about what I was drawing, thinking about something else completely. Content. Sometimes I look at my friend's art, and wonder at the hours they spent honing their skills from a young age that have all built up to this. Not just skills they learned if they attended an art college, but years and years of discovering and learning on their own. You learn very quickly on your own then, building a lasting relationship with your paints and pencils that won't let you down. Sometimes I think that most of my illustrator friends draw like they did when they were 12. They've just continued to build around it since.
I remember the way my classmates used to draw when we were in school. I could identify their pictures on the walls like i could identify their handwriting. The general perception I believe unfortunately, is that drawing pictures is something you do when you're young. But why on earth should you stop when you "grow-up"?