How much money (real world money) are you willing to spend on the game?
If your answer is A LOT, then buy hundreds of dollars (or whatever your local currency is) worth of donuts and use them to charge the XP Collider to multiply your XP income.
If you answer is NONE, then:
Do your quests.
Keep all your idle characters on tasks to earn money and XP. You also need money to level up - each new level requires buying a least one building and they get more and more expensive with each level. You're gonna need land to put those buildings on, so you'll need money for that, too.
Piece of advice: Don't buy a bunch of land and gobs of decorations right away. Land and (most) decorations don't earn money or XP. Buildings and character tasks DO earn money and XP.
Buy as little land as possible and just cram your building into it until you reach the current level.
Put your characters on the shortest tasks that match up with your playing schedule. If you're not going to be back in the game for 4 hours, put all your idle characters on 4 hour tasks. If you can return to the game in an hour, use 1 hour tasks. Overnight use 8 hour tasks. The shorter tasks earn more money per hour, but if a character is going to sit idle for 3 hours after a 1 hour task...
When you have quests to complete put your characters on tasks to match as closely as possible. Many quest tasks are odd lengths - 3, 6, 10, etc. When you finish a quest task you'll often need a different character to do the next task in the quest, so you'll need them free to do it. Yes, you can often break a character out of a task by storing their building (not Homer or Lisa though - you can't store the Simpsons House), but then you also lose the payout for that building since the timer starts over when you put it back in your town.
Get 100 neighbors and visit them every day. You'll get Friend Prizes- including characters with tasks that earn money. And once you get all the Friend Prizes you start getting random Free Donuts for tapping in neighbor's towns. I've gotten hundreds of donuts that way and I've only been playing a little over a year.
There are lots more suggestions on how to level up as quickly as possible. Check out the Game Discussion Forum in the official EA Simpsons forum group for more tips and advice.
