About your work shown here,, Try to follow many tutorials and over time you have to find your own style and go your own way after learning the basics,, For your first ever GFX this is pretty good!,, don't be discouraged when seeing better GFX,, No one started out as an pro
Also you can find allot of inspiration from work of other artists,,
But you're going the right way!
Pretty good thoughts and designs you got going on.
Constructive Criticism:
The stem on the flowers.
I would change the effect on the mario to maybe a red or blue and have it blend from front to back and within the render (mario). If you fix the flower, i'd say it would be an alright desktop background for you, maybe swap the color around a bit or whatever you like, your design.