I was studying Industrial Design where 3d is part of the process. After finishing my studies and working for some time, I decided to specialise in 3d visualisation.
I usually get a brief which can be from a simple stick drawing to a very detailed illustration. I envision on how it should look like fairly quickly and find reference images. After that, it is the standard process of modelling, texturing, lighting, rendering and retouching. Unless you have never done anything like it before, then it is research and possibly quickly learn new software. :)
Think about what you would like to do with it and by that I mean if you would like to work for movies, games, animation etc. Learn the tools required for that field and keep going with it. 3d is mostly about experience.
I actually like my personal projects the most, which would be the cat and the squirrel. Simply because that is how I learned fur and where I had the time to put all my energy into it.
The main software I work and render in is 3dsmax with Vray, Zbrush for sculpting, Photoshop for texturing and retouching. These are the ones I would use on every project. There are a lot of other plugins and software but there are very task specific.
3d is a very broad field. No need to know everything. Do what you love and specialise in that.