Helos are like most other units: to use them effectively you need a lot of them. Say you have a maginot line type stalemate with your enemyyou've got peace but only just so you have a whole bunch of infantry fortified on the border. But you only have tanks and modern aromor is a long way off. You have tried and failed to make a breakthrough with cavalry and artillery. So peace sets in just to keep the peeps happy.
Lo advanced flight. build maybe thirty helos, station ten in each of three border cities. load with your best infantry units. Send fighters out on recon and to probe three or four cities to see if they have fighter cover. Station a bucketload of bombers in your border cities too. Fly the helos out to drop a line of infantry deep in enemy territory. Now use bombers to try and take out the rail and road that lead to where you have dropped your inf. set all the inf you have standing on the border to walking and get them to take the artillery with them.
You have just encircled a patch of enemy territory with strong infantry. Just tighten the noose and that territory is yours. Attack the cities from as many fronts as possible. Repeat and rinse.
Another good use for the helo\infantry combination is establishing a bridgehead on a far shore. Rather than sending out a whole parcel of marines just send out a transport with one settler and three good defensive units and four artillery. artillery. Drop them on enemy territory, preferably in a jungle or a forest or on a hill.. Land the settler alone if your enemy is not aware of your intentions or in a gap in his border if you can find one.
build the city and load up some helos with infantry, fly them in and unload them. Unbeatable bridgehead unless he has a nuke and is willing to use it. If you have Computers build a barracks and upgrade your infantry as they arrive. You can bring in as many infantry as you have helicopters every other turn. Plus when you run out of infantry to move about they disband for twenty five shields a turn, cheap way to get that airport built.