The Simpsons: Tapped Out blends different free-to-play models to allow you to run the kind of Springfield you want to run. Yes, you could drop real money on the game and unlock your favorite characters and landmarks right away, but with a little planning and a lot of foresight, you won't have to spend a dime.
The first thing you need to do is understand how long things will really take and realisitically assess when you'll be able to revisit your Springfield. If you're checking in after a long break (like overnight), you'll want to collect the money from your citizens first. This will allow you to send them on short, <1min tasks that will be completed by the time you, say, collect all the money from your buildings.
The next thing you need to do is organize the townesfolk around the overarching level goals. If you have to assign Cletus to dig through the garbage for a mission, you should organize the rest of your residents to like-timed tasks. Don't give Lisa an 8 hour assignment when you'll be back in Springfield for a 60 minute Tomacco harvest.
Be mindful of the way your buildings are operating as well. Some buildings take a longer time, but they can very easily factor into your time management as well. Run your Springfield like a well oiled machine and you'll be richer than even Charles Montgomery Burns.