Assorted related tips:
* Build 2 airports on the receiving continent; if you end up in a prolonged war, the disorderly mob almost seems to always destoy the airport. Keep a few extra troops in the airport cities to quell the mob.
* Esp for a big invasion, dont depend entirely on airports; you'll still need transports for arty, workers, settlers, cruise missiles etc.
* A steady stream of materiel is nice, so rather than convoys of 3 transports once in a while, try to have one transport depart every turn or every other turn. This helps from having all the transports on one side of the ocean when you really need one on the other side, RIGHT NOW.
* A harbor on the invasion continent is nice to have eventually, in case you have to heal ships. The harbor and airports cost maintenance gold but they also provide food and commerce benefits to the cities.
* If there are enemy ships about, you'll need to guard the transports more closely, but can use this as an advantage (esp if transport capacity is more than you can build). Sending 4 transports across, with 3 empty as decoys, has sometimes SEEMED to 'scare' the AI as to the size of the build up. In this case, travel along the ocean territory border so they can see (unless they have a strong navy). Doesnt seem to work if they have a spy, obviously.
* If there is a strong naval threat near the transport lanes, it doesnt hurt to half fill transports and send 2ce as many per trip. Better to build extra transports than loose 8 tanks to a frigate you didnt see.
* Unload transports in cities in case there are subs around to see the contents.
HTH