Fast population:

When creating a city, put down a large city, start expanding it, take out all the small houses, and keep expanding. When it takes a lot of clicks before it increases population (usually around 30,000), put a small city as close as possible, even if it touches. Then, delete the small city and the large city's population will stay the same even though a portion of the city itself was erased. This may be repeated until about 70,000, at which point it will revert back to 0.

Faster trains:

If you have a long train that takes a long time at stops, make sure you have a train orientation depot on your track. When it stops at a station, let it unload/load at a station, then press the button with a train on it. Then the train that is at the stop. Press the button to turn it around if needed, then finally press the button that takes the train to the depot twice, It will leave the stop and go to the next one.

Eliminate CPU buses:

Build a snaking railroad line over the bus route. The train will destroy the CPU buses, but will also eliminate your own trucks and buses.

Eliminate CPU airplanes:

Build a tree covered tall hill at the end of the CPU's runway.

Hints:

Build a tunnel from one end of the map to the other and the tunnel will be so expensive that the price will get a negative amount that will be added to your account.

To ruin a good road network for a competitor, simply place a rail piece at right angles over a piece of road, then use the bulldozer to destroy it. The computer will not rebuild it