Well there’s not much to suggest on. It appears intentionally minimalistic. If we say to add detail to the marshmallow man he’d would move away from looking like a marshmallow man. We could say add an environment but obviously you made the decision not to embark on an environment, its not like “oh your right i totally forgot about the background!”
I think you’ve finished a project and now it’s time to start a new one. You usually learn a lot more in the first 3/4 of a new project than refining an old one to hell, so for a beginner it’s probably good to just finish one and move on to a different one without spending a lot of time making them perfect. That’s just my opinion anyway. Just don’t leave projects less than 1/2 that’s a no-no :).