Experience. Whatever area you want to work in as a consultant, you must be able to show clients that you’re qualified to advise them. If there are organizations related to your field, make sure that you’re a member of them. Similarly, if you can take a course and become certified or registered in your field, do it and then add that to your credentials.
One thing, though, there is a big difference in making an app for Android and an app for iOS, and that is the fact that making an app for Google Play costs just 25$ one-off, making an app for iOS costs 99$ a year, so if you are making an app for iOS, I will recommend you to be a bit more confident about the way you will make money by your app, than if you are making an app for Android.
Another obvious option is for people who enjoy writing. There are countless requests on sites like Elance for all different types of writing. Polish your writing ability and then start bidding on some of these writing jobs. At first, you'll be doing this a few hours a week, but over time, you can build up a dedicated clientele and make a full-time living off your writing.
FlexJobs, a search site for the best work-at-home jobs, reported in their The State of Remote Jobs survey that, as of 2017, 43% of U.S. workers now work remotely — even if it's just a part-time side hustle to supplement their income. For remote jobs, you'll need a computer, some basic skills, and a can-do attitude. And yes, even nurses, teachers, editors, or graphic designers can find countless of opportunities for work from home jobs.