It seems like you can get a huge bonus for putting certain buildings together and creating a "Specialty District," although I've also seen this called a "Combo."
There's a pretty exhaustive list of parts of the game in this Google Doc spreadsheet, which might be enlightening reading, although it's a bit dense.
I found a list of combos in this message board post. I don't believe it's 100% complete, but it might be enough to help you figure out what the pattern is:
- Pleasure - Casino, Arcade, Bowling Alley
- Health - Hospital, Sports Gym, Spa/Jpn Rest
- Shopping - Supermarket, Boutique, Jeweler
- H. Springs - Jpn Rest, Woods, Lake
- Culture - Jeweler, Art Museum, Movie Thtr
- Gourmet - Sushi Bar, Chinese Rest, Bar
- Student - Trade School, Steakhouse, Diner
- Fashion - Boutique, Art Museum, Drugstore
- Business - Office, Office, City Hotel
- Intellect - Bookstore, Trade School, Art Museum
- Geek - Elec Shp, Anime Shp, Game Shp
- Kids - Toy Str, Park, Game Shp
- Tourist - Woods, Mountains, City Hotel/Jpn Rest
- Local - Cake Shp, Greengrocer, Florist/Fish Monger
- Industry - Scooter Shp, Car Dealer, College
- Date - Theme Park, Zoo, Movie Thtr/Arcade
- Sports - Stadium, Bsbll Field, Sports Gym
- Nature - Pasture, Park, Woods/Lake
- Lunch - Cafe, Deli, Bakery
- Silicon - PC Shp, Mobile Shp, Game Co.
- Ancient - Monument, Pagoda, Jpn Garden
- Animal - Zoo, Pet Shp, Pasture
- Media - Antenna, Concert Hall, TV Station
- Fishy - Fishing Pond, Aquarium, Fish Monger
- Hacker - Pizza Parlor, Fast Food, Security Co.
- Rock - Record Str, Video Rental, Concert Hall
- Ghost - Skyscraper, Skyscraper, Skyscraper/Antenna
- Hollywood - Movie Thtr, Theme Park, Jeweler/Boutique
- Special - Airport, TV Station, Office (M)
There's also this page which purports to have some help information on it, but it looks like it just might be a transcription of the help files in the game, so I don't know how much value that will add to you.
I also found this thread, which covers (I'm guessing) the Japanese version, but I bet the core gameplay is the same.
In one place I found a reference to something called a "house combo" but the tip was unsourced and I couldn't find any other reference to such a thing. If you're still stuck after mastering Specialty Districts, you might try to figure out if this is possible and how.