I describe yellow as bright & cheerful. Here are a few objects that have different shades of yellow: school bus, lemon, rubber ducky, bumblebee & banana. Try sketching these objects then coloring them with a variety of yellow tones.
Instead of drawing single lines, try drawing double lines. Start with your favoritie drawing tool (markers, crayons, etc...). Choose two different colors. Hold both colored drawing tools in your hand. Write your name with both colors. You've just created an art with double lines. It takes practice. So, keep practicing. Try shapes. Experiment with 3 colors to create a cool art.