We always quarantine for a month, then put the new one(s) in a wire rabbit cage in the house for a few days to let everyone see each other, then late one night go in and put the new one(s) on the roost with the others. It is not fool proof and at times there are still "pecking order" issues but it tends to lessen the severity of the introduction. At times a good mature rooster will also assist in the introduction of new hens.