Farming for lower level legendaries

In general if you farm NPC's around the same level as the iLvL of the item you want you will have a greater chance of getting it, the logic being that if you want a level 14 item, you increase your chances of one dropping by reducing the chance for items higher or lower than level 14 to drop. There is no simple one-paragraph answer but for anything that's is worth farming at lower levels there will be a guide on youtube showing you how to farm it as the above poster mentions, if there's no guide it's not worth the time to farm.