I've seen a lot of successful entrepreneurs fail as investors in start-up companies, most because they make at least one of these mistakes:
1. They invest in good ideas rather than good founding teams.
2. They expect the same pace, the same rush they experienced running a company. When they don't get it, they grow impatient. Then they get destructive.
3. In the hour or two a week they spend on their investment, they try to be the CEO of the company.
4. They invest alone as opposed to in a group with other investors. They don't spread the insight, the burden, or the risk.
Do the opposite.
Accept that you are now the tail, and you are not wagging the dog. Your founders--they are the dog in this metaphor--want your experience, your wisdom, and your contacts. (And your money; that's a given.) Give generously of those things and accept the parameters of your role, and everyone has a chance at success.
As told to Inc. deputy editor Dan Ferrara.