You will want to look at getting insurance, since most clubs/gyms/studios I taught at required me to show evidence of this (will cost around $200). There are a couple of companies that offer it specifically for yoga instructors but you will generally need a certificate to show at least 200 hrs teacher training to a standard (check out american yoga association for their membership details, I think this will cost around $75 annually - but this was a couple of years ago).
I found having a website helped, having a few business cards or flyers printed to handout. It takes time to build up a good reputation and a collection of students who will keep coming to your classes. It also takes time to build relationships with the locations you wish to teach at. If you want to teach at a studio it helps to be practising there a while so they can get to know you. Also, it is tough to make yoga teaching a full time job, unless you work long hours (sunrise to sunset) and most if not all days of the week. Also factor in travel time and expenses (travel, equipment, music, class handouts if you do these). Most yoga teachers work another job part time as well.
Om shanti. All the best!