have a read up on region play, in order to get your city into some epic proportions that's a really fun way to play.
So the basic premise is start a city close to a corner of a map, start zoning for light residential and industrial, then add a road link to a neighbour region.
Exit the map and start in that new region zoning for heavy/medium industrial. You can stick your coal power plants etc in this new zone which will basically be a dirty industry/pollution zone.
Because there will be high demand for jobs here people will leave your city in the starting region to travel here to work.
You get the benefits of the jobs but none of the downside of the pollution.
As you started your main town in the corner you can now do a similar thing with commercial zoning. Get a bit of demand in your initial city then make a link to a bordering region and make it your commercial region.
Just google some region play tips and you will see lots of advice.
You end up with different regions catering for different needs of your sims.