Well, that's what I do for a living. I have owned a lawn care business for 12 years. Of course there are many factors. Will you be doing this legally, as in paying income taxes, carrying liability insurance, and collecting sales tax for the state? In my depressed area the minimum price for full service lawn care, which includes trimming and blowing, is $30. A high school kid might do the same yard for $20, but he doesn't have the overhead. Imo, you need to charge $25/man hour as a bare minimum.
Realtors aren't a great way to go for someone just starting out. They will require you to have liability insurance, and worker's comp. They also expect the cheapest possible price, and are notoriously slow payers. I cut 75 yards for a land management company, and they haven't paid October's bill yet.
I am a member of Lawnsite.com, and as far as I'm concerned, it's not a very good resource, but certainly check it out. Napa is right about it being a cut throat business.
It's important to realize what it costs you per hour to work, and charge accordingly. A good truck,trailer,and equipment could easily set you back $60,000. Also, most people want someone who will take care of their leaves in the fall, and clean up in the spring. While many people will pay more for a professional job, most are looking for the best price.
One last thing, you cut grass, and mow a lawn. Good luck to you. If you have any more specific questions, don't hesitate to ask.