1) Don't go into debt - Start Small and work Big; if you cannot make a profit being small; you probably will not be able to make a profit being large.
2) If you do your business plan and your calculations show you making massive amounts of money in the first few years; realize that you probably are way off in your calculations and need to do more research. There is way too much competition out there to make super high profits on just about anything. Competition brings prices down, so don't expect making $100,000 profit in your first few years. In fact if you think you are going to make this much, I would bet you are ill prepared to start a business.
3) Starting a business is easy money. This could not be further from the truth. When starting a business you have to do something you love because you need to spend every minute working on the business, thinking about the business, dreaming about the business. You need to make your business your passion and your obsession. If it is not, then you are probably not going to make it. To make it succeed, it takes just too much effort to do if you are not passionate about it.
4) Take it slow; just like a new girlfriend sometimes you become infatuated. You don't marry your girlfriend after one month of knowing her; take some time to do some research. In fact, I would recommend spending at least year doing research on the business plan before spending any money on it. Then after a year, if you are still interested in it, spend a little money and do it on the side until you learned enough and become profitable enough to do it on your own.
5) Everything takes twice as long and costs three times as much as you thought it would.
6) If there are no barriers to entry "such as lawn care or painting"; expect small profit margins - especially now in the recession
7) Save up money prior to starting, not only do I recommend not going in debt. I also recommend at least having a year worth of disposable income in savings as a buffer; incase things don't go as planned. The other option is to find a sugar momma or daddy so that you can rely on their income to support you when things don't go as planned.
8) Get the "buy in" of your family; you will need their support. It's too hard to do it alone.
9) If you think you cannot lose money, run away from the business idea and don't look back!