A good friend of mine started his own shop about 2.5 years back. He was working full time at a shop, and started taking on sidework for family and friends. Word of mouth spread and he eventually had his hand in so many cars he got multiple notices from the county for zoning violations. After the year of so of doing this, and a pretty nasty falling out with his boss, things aligned for him to open his own shop up.
He got a single bay shop that had one lift, with space to work on another car ahead of it on the floor and that was it. The other half was shared by a Mom and Pop delivery company. He was very fortunate to have his nephew (how I originally met this guy) graduating high school at the exact time he was thinking about all this. He sold his '69 Chevelle that was in mint condition for about $10,000, had about $5,000 saved, and got an investor for the rest.
Last summer he moved out onto his own, 3 bay shop, still him and his nephew. They work basically whenever but this is mainly due to him being single with no family, but it allows him to bring on jobs people need done that night, or ASAP. He manages the maintenance on the fleet for the company he used to split a shop with, and another fleet across the street. He usually has 10-15 cars on the lot at a time for any given thing. When business get's slow, he starts buying wrecked cars that need a little loving, and then sells them. Actually had a pretty awesome article written about him. One of the most talented men I've ever known, and will likely ever know.
I know one of the key ingredients to his success is knowing the most common cars inside and out. He was loyal to loyal customers, and would frequently give them some sort of incentive to stick with him. Would always be honest with his time, and would stick with his original estimate, unless it was an extremely drastic difference that you simply couldn't forsee and wasn't really anyone's fault. Even then, he usually only charged them for half the time extra he actually had in it. The biggest reason IMO for his success is he would take on jobs no one else would want, and if they did take them, it would be for an outrageous amount of money and take forever to do it. I pulled more engine's, dropped more transmissions and pulled more heads with this guy in a years time than I think I ever will for the remainder of my life.
Wait...Did I mention he is paralyzed from the waste down and confined to a wheelchair?
http://hhcourier.com/main.asp?SectionID=8&SubSectionID=33&ArticleID=157262
http://tdn-net.com/main.asp?SectionID=152&SubSectionID=255&ArticleID=104112
http://tippgazette.com/index.php/tipp-city-news/70-paralyzed-mechanic-lives-his-dream