What do you want to do? Be a footwear designer or just make a lot of renderings?
If you want to be a footwear designer you need to show process, thinking about manufacturing, market analysis, etc. you may not have the knowledge of someone in the industry but showing only renderings is no excuse. So some research. Cut up shoes. Figure out the details and show your thinking process. A rendering does none of this and is pretty useless aside from showing you can make a nice rendering.
R