Start with a problem
It's much harder to start with a solution and then find a problem that it can solve
Know the problem clearly
You want to be certain that the problem exists before building anything.
Find the people that have the problem
The people who experience the problem can give you a clue to how to solve it.
The problem must be solvable
Because not everyone can build a SpaceX.
People should be actively solving the problem
Other people solving it means that the problem actually exists.
People should be spending money to solve the problem.
Mo' money, Mo' potential for profit
Read helpful tweets from product designers—like Paul Graham & Sam Altman from Y Combinator.