They are successful business-people, with equity to invest. Since they made their money growing their own businesses, their natural advantage as investors tends to lie with investments in small growing firms. Rates of expected return, and levels of security needed, can vary widely. One eminent scholar of entrepreneurship has found that some angels invest primarily for the thrill of participating in young, dynamic ventures, but most are careful and sophisticated investors. The potential recipient of angel investment should look for wisdom as well as money.
Angels can help as mentors, coaches, network introducers, etc.
The angel market is largely unregulated, and some owners have found that some angels appear to have horns and a tail. If the owner screws up, the angels may move quickly to take over and to protect their investments. The best way to manage that possibility is to talk with them often, and learn from their experience and advice.