Glen Moyes (Metsys on the forums) has written an excellent article on the key steps to becoming a great 3D artist.
He writes about the importance of mastering a tool before taking on a more complicated project, about the importance of being an artist before being a software user and about the process of designing art that captures the attention of your audience.
To me, the essense of his article is this:
Blender is a tool, not a process. If you can't make something good without it, you won't make something good with it. It doesn't enable you to create a well-designed image without first being an artist and understanding the principles and elements of design.
This is one of the most insightful articles that I have seen in the Blender community during the eight years that I have been around. Please do yourself a favour and take 30 minutes to read it.
Link: To Those Learning 3D