though this is posted elsewhere ill review what it takes to get big bonuses.
late in the game:
1) great distance
2) size 20 city with every square producing trade, both for source and destination cities.
3) democracy, both source and destination.
4) superhighways at source always but also destination unless the destination city is all ocean tiles.
5) airport both cities.
6) supply demand requirement met. uranium is by far the most lucrative.
7) freight rather than caravan.
8) overseas trade route.
in the early game:
1) first 200 turns get a bonus.
2) certain techs not yet discovered results in a bonus. dont recall which but it might be navigation and engineering.
3) source city has built or rush built all of the following: collosus, aquaduct, sewer system, and harbor AND is size 20 with all tiles producing trade. if demo isnt discovered yet then at least republic. ideal destination would have as many attributes of the first list as possible. best plausible destination is size 12 republic.
you can increase your bonuses enormously if you:
1) road up the destination city even though its the "other guy's" city.
2) chop down trees at the destination city.
3) find one without hills which they might mine and of course mined hills produce no trade.
4) try to find a peace oriented destination civ with a good chance of staying in democracy. given that you cant guarantee he will stay there try to find a destination city near your opponent's capital.
5) rehome your units to your supercity.
6) play on a large map.
you can decrease time to destination if:
1) your supercity is on a coastal square
2) if you road your empire. then railroad.
3) you research lighthouse to give your triremes the shortest possible route.
4) you make a point of prioritizing naval research.
5) magellan's of course.
6) destination city on a coastal square.
7) ... or if you cant get a good coastal square then road the coast up to their city.
8) later in the game airports to get a 2-turn delivery.
early trade routes from a size 20 supercity to a city that demands the goods frequently net 800 gold delivery bonus (and 800 beakers). those 800 gold will rush build two more caravans two settlers AND a ship. this is why i rehome them even though it leaves me with an empire paradoxically almost without any trade routes
some wonders will make this strategy more efficient:
1) hanging gardens so you dont have to rush build temples.
2) pyramids to speed up the production of settlers.
3) collosus to improve trade bonus
4) lighthouse to speed up triremes and reduce the numbers needed.
it goes without saying you will build others like leonardo's when you get the tech but they should be trivial. the first four are NOT trivial. it takes skill and luck to get all four on a deity game.
the fastest net-worth growth achievable during this stage is about 10 percent per turn or a doubling every 7 turns. its possible in a good game to convert the large worldmap to grassland by 1850 - which is if i remember correctly 230-235 turns.
, but it was a very big map).
to make it work? 
Couldn't find any trade routes. So, are there some games where it works better than others?
[he wrote "despite how much fun i've had constantly crushing opponents on king..."] so maybe we need to clear up which tips apply to that goal.
(and not much more). I set all my tiles to specials or ocean squares until my city was making about 6-7 arrows. It was NOT a SSC, of course. I found an AI city that demanded hides (or whatever) and travelled about 15 squares across the seas to get there. No idea what it's trade was like.
