Wow
You have a LOT of promise so ill give you some tips. Try using less saturation, bright vivid colors are good sporadically but too much and it wont look right. You need more shadows, less saturation but more overall brightness like a light source. Make your shadows with a bit of gray.
You have the same problem i had and its making a distinction between light and darkness. But keep these tips in mind and youll improve a LOT, goodluck :D