Super Mario Bros custom tileset

[Garamonde]

the colors on the mushrooms, pipes, green bush and that sharp-cornered grey wall thing beside the yellow water(?) need more contrast, and all of your shading could use some hue shifting.
(by the way, idk if the Spriting Dictionary has been linked already but I'm linking it now so you can learn about all this stuff easier.
it's not bad for a start though!