I bought Joanne Sharpe's book "The art of whimsical lettering" - one of the best books on learning to doodle and play with lettering. Most books spend too much time explaining what supplies are needed. Joanne jumps right in, urges you to use the supplies that you already have, and gives you 25 mini projects to practice. And she encourages us to make mistakes - yeh!
Here's page one of my play journal