Finally, a Third Bet, which fits most new business candidates (if you are not applying your First or Second Best Bet), would be to choose a relatively random line of business after exhaustively studying research and financial models on emerging industries, even if you have no personal interest or history in that particular line of business.
Be creative. Pick an industry that is not fully developed but has a lot of potential. Think about less sophisticated or glamorous business niches since they are more likely to be overlooked by potential competitors.
Make Millions and Make Change!
