Good work! If you're looking for advice, I'd highly recommend defining a palette before actually drawing. It doesn't necessarily have to be yours (in fact, there are many great palettes here on Lospec that you can use!), but just having a set palette (preferably one with low colour counts, like 16 or less for beginners) is a really great way of learning how to be deliberate and smart with your colour choices, and it leads to more cohesive end results. Hope this is useful!