What shape works best when drawing the eyes and mouth?

You can do any shape you want that looks good to you. For example, I would mostly use a bubbly oval since it is a cartoon. You can also draw a big upside down U with a slightly bent line under it. If you want a chibi face, you can try searching the internet for instructions on how to draw anime eyes. For the mouth, you can draw either a normal smile or an upside down triangle to make it look like it is smiling with an open mouth/laughing. You can experiment! If it doesn't look good the first time, don't give up. Practice makes perfect!