Can you show us some sketches to see how you construct your art, please?
At the moment, what I can say is that you have a cute art style and you seem to have a good eye for colors
I can also say that for shadows you use mostly soft shadows. Using both soft and sharp shadows tends to improve a lot the render. Sharp shadows are basically shadows with sharp edges, they are use for more intense shadows or for materials who gives sharp shadows (metal, shiny plastic...). You can use both sharp and soft shadows for one thing too (for skin for example it gives a nice render). My advice would be to use different kind of shadows, and to also use sometimes only sharp or only soft shadows to find what you like the best
I hope that helps! Keep up the great art!