If you want to get rid of mites,fleas and ticks on your chickens, then you will first need to bath them. If you can find a mild shampoo that would be safe to use on your chicken then that would be a good idea. If not then just bath them thoroughly with warm water.

Once they have been bathed, place them in a clean, seperate place to where they are usually kept. You will now have to ensure that their living quarters and around their living quarters are cleaned. Use a disinfectant that is safe for your chicken and throw away any bedding that was being used. Literally everything needs to be cleaned to ensure that you get rid of the mites and fleas completely.

Once you have done this the chickens can then be placed back into their living quarters. Ideally you should look into the reasons why your chickens may have the problem in the first place so that you can avoid it again in the future.

 If they are in a pen put seven dust all over them and the ground. They'll roll in the dirt. Once every two weeks, and when they're gone once a month!

 I too have used sevin dust effectively, spreading it all around the pens, and even lightly dusting the birds themselves.