Pretty much self explanatory but there are just a few things to mention.
- Make sure the farm alliance you are hitting is closed and there is no enemy to reinforce against you
- Do not exceed hospital capacity to loot farms
- Use cavalry and infantry as they have the largest capacity and also move faster
- Hide the archers and mage in the alliance fort or a bubbles castle
Remember to remove the troops to empty your farms the most effective method for troops removal is as follows
Set a 30minute rally onto the ancient ruins. You can send your beast like this where as you can not if you send out to gather whilst you loot. The other downfall to having all troops gathering to be able to loot is that you have to recall the farm defenders that you leave home to start a battle.