I'm guessing you mean in Tapped Out (hence the rename of the question).
Send all your characters on jobs. If you can constantly check back on the game periodically, send them on tasks for that time period.
Premium characters, those who cost donuts to buy, give more money than non-premium characters meaning they can get you more in the long run.
Most premium decorations give you a bonus to your overall job money received. The more donuts, the higher the bonus. The Whale gives a whopping 7% bonus to all character job payouts. This doesn't show in the menu but you gain it afterwards.
Then obviously, there is buy as many buildings as possible and get their cash periodically.
Of course, you can also buy cash with donuts but that's not really efficient. Also, doing quests often rewards you with cash.