Most of the time, I find that there is no one way that is a perfect fit for everyone when it comes to deciding what job types they think they can do at home.
The most logical method is to simply spend a little time online, doing general searches for other people who are working at home, see what kind of jobs they are doing, identify an idea that is based on your current job or skill set, and adapt that idea to your own interest, skills, and ability.
All too often, we tend to look outside of our current job environment and meet with frustration because we cannot come up with a suitable idea for finding or creating a work at home job.
But working at home takes creativity in large amounts, so don't fall into the self-imposed trap of wondering how you are going to have time and money to learn a completely new trade, skill, or complete a degree before you can start working from your home.
Instead, take a good hard look inside your current situation.
Think about what skills you currently use in your existing job function, or may have used in the past. If you currently work in the billing department, and have a good head for numbers, you most likely already have the hands-on skills you need to perform a number of administrative, accounting, bookkeeping, and general assistant duties, as so many of these job functions can overlap, generally speaking.
Another important point to remember is that some jobs are just better suited to be performed from your home than others.