I careless about trophies, i only care about getting new troops and upgrading D. Not all of us have all the cool different units, or upgraded to level 5+
The highest barracks level req to have a moderately useful farming army is 4 to get the giant. I don't have a single level 5+ unit, but either way the idea behind farming is to spam and grab as much as you can as quickly as you can without caring too much about how much you can actually destroy.
Some people just spam an army with is 75-80% goblins and the rest giants, it works just as well for farming but you are a lot less likely to get a star. Everyone can farm effectively, it just takes some practice. You have to be willing to waste some gold finding a good target (a target in your range who has a poor base setup or who has a town hall that is wayyyy higher in level than the rest of their stuff) and the patience to see great gain in the long run. It's all about prioritizng what resources you really need and focusing on getting as much as you can out of a single target.
Even just making some lightning spells then dropping all of them straight onto an enemy resource storage structure is enough to get an amicable return. I only farm Dark Elixir now and I do it with this method. I hit as many of the people who have already hit me as I can via revenge then I attack 1-2 targets through the battle finder to get my trophies back up.