Lord Parkin
aka emperor
My advice would be simple: focus all-out on economy for now, tech like mad, and hit them as soon as you have a major advantage (for instance, if you manage to have an oil-based army and navy a few turns before they do). A technological advantage, even if only held for a few turns, gives you a massive advantage in the initial assault - and thereby makes the rest of the war a whole lot easier.What would be the most important concerns for an intercontinental invasion of another continent whose ultimate goal is a conquest victory? I'm alone to develop on my own continent(decent number of prod cities, lots of cottage cities), and I'd like to keep important considerations in mind before I make contact and eventually wipe out the other nations. Things like how many ships to build, diplomatic moves, etc.
Also, if at all possible, go for the top dog first, then take out the next highest ranked guy, and so on. This way you don't end up with a civ that runs away with the lead and claims a space or culture victory ahead of you. At the very least, if you work your way up from the bottom tier civs, you could end up with a very powerful and dangerous rival by the time you get to the last guy.