1. Art Knowledge:
Study the basics such as color theory and perspectives. Studying these things helps determine the right form you want and create what 'makes sense.' Experiment with colors such as complementary, tertiary, and any other color combinations.
Understanding your tools help you be more familiar about what can be done. For example: if you don't know how to blend images into the background effectively, then you should search up how to. There is no right or wrong answer to this. Each artist has their own form of steps to reach their goal.
Everyone has different tastes in this matter of subject. For one person, the wallpaper may look beautiful, but to another, he/she may not be interested at all.
DO look up tutorials
DO create something that may be popular for others
DO get familiar with certain techniques shared in guides on the internet
DO promote/share your art (Without spamming)
DO search for other ideas or references
DO start your design process as a sketch first
Do NOT steal/use someone else' work without a valid 'yes' after asking for permission
Do NOT use stock images that are copyright protected/not free (Even if it's 'royalty free' - but 'royalty free' does not mean free)
Do NOT just drop the rendered images on your canvas and do nothing to enhance it! Most images do not have the proper use of lighting for it to be realistic/blended