Start by getting out some stencils and Sharpie markers.
Hold the stencil with one hand, and trace the shape with your other hand. Make sure you hold it very still! Otherwise, your shapes will be wonky.
Design your own castle, town, or city. Have fun!
Next, get out your watercolor paints and a cup of water.
It's important to keep your brush wet when using watercolor paints. They're called WATERcolors for a reason!
Be soft and gentle when stirring up your paints. Don't let the metal part of the brush touch the paint. Only the soft bristles. If you're too forceful, you'll smash it all to bits!
Be gentle while you're painting, too! Only let the soft bristles touch the paper. If the metal part of the brush touches your paper, it'll scratch through and poke holes in your painting!
Use the same colors in multiple places, but think about balance. For example, here I have ONE orange shape in the top-right. Where should I make another orange shape?
<--------------- Over there! A second orange shape in the bottom-left balances the one in the top-right!
Pick one color that you want to use A LOT of, and spread that color all over the place. Here, I've used red and pink in 10 different shapes! This brings unity to the picture, making it feel like all these buildings belong together.
But you don't want EVERYTHING to be the same! Add some other colors for variety, to make the picture more interesting. And don't forget to paint the background!