Pick something easy or achievable for your skill level. Obviously if you have only watched a few videos you are not going to create the greatest artwork ever made in a short time. With that being said, you can create a great artwork for using the knowledge you have gained.
I would pick something you want to learn like modeling, shading, lighting etc. and apply that to whatever you do. Pick something up off the desk where your computer is and try to model it. Try modeling a rock and see if you can even get it to render for example.
Blender has a large array of things you need to learn individually before it all clicks into some of the gallery images you see online.
When you give a solid effort and learn something new to apply to the next attempt, there is no failing. If you can’t come up with something from scratch follow along with the tutorials until you build habits that allow you to come up with something from scratch later.
