each type of troop can carry a certain number of resources from a raid. check the manual to find out how many yours can carry. so if you send 2 troops on a raid and they get a full load of whatever they can carry, then you should raid again, in small groups, until you don't get full loads anymore. rinse and repeat 8 million times to win. the whole game is raiding at this point, you can produce way more resources from raiding than you can from your resource fields.
raiding places you haven't raided before, always send a bigger group, because you could lose 1 to the rat. there are a certain number, somewhere above 10, romans is 12, where if you send 12 troops against the 1 rat, you don't lose any.