I hope I can make this sound as simple as it is. -- Normally in the instructions, they have you heat up castor oil, put lots of it on your abdomen and torso, put large cloths over it all, heat up water on the stove for the hot water bottles to make it nice and hot, put a large piece of plastic sheath over the cloth to keep it from dripping, etc., etc.
My philosophy, which stems from quite a lot of personal experience, is that this is way too complcated, and surprisingly, somewhat counterproductive. I've found that the excessive heat that is normally called for is hard on my system. The time involved in preparation can also discourage me from doing it at all. Also, no matter how hard I try to not have it be messy, it almost always is. So here's what works really well for me.
I fill up two hot water bottles with hot water from the faucet. I put the bottles on my bed with a wrapped up old blanket over it. I lay down on the top of the bed and put a separate blanket over myself from the waist down, in a way so that I can easily pull it up after I apply the oil on my torso. I then place a section from an old towel (about 1' x 2') and place it on top of the blanket.
I then apply a relatively small amount of castor oil (about an ounce or so) over my solar plexus area, and then rub it with just one finger over the rest of my mid-section. I only cover an area the size of a small plate or so. -- I then immediately put the 1' x 2' towel on top of the castor oil. -- I then put the hot water bottles on top of the towel and the wrapped up old blanket on top of the bottles. -- I then pull the other blanket up over it all. I'll spend as little as 20 minutes per session, or an hour or more, especially if I go to sleep (happens fairly often).
I can do this all without it being messy because I only have one fingertip that has gotten oil on it. And I feel I'm pretty strategic about that as well.
I rub the castor oil residue from my fingertip onto my eye area (including eyebrows), and also including over the eyelids, as the oil is good for both. I also rub a bit around my whole face, as I've read that putting castor oil on your face can make a person look ten years younger in very short order.
BTW, I use a castor oil bottle that has a squirt top, so I don't have to put a cap back on. After I apply the oil, I put the bottle on top of a used yogurt container lid on the dresser next to my bed. There's always going to be a bit that drips from the bottle after applying it. -- Let me know if you have any questions!
Also BTW, I talked with a chiropractor once who had a clinic with a sauna in it. He originally thought that to get the full benefit of a sauna, you had to have it quite hot, and had to do it for a good amount of time, like 45 minutes or so. He told me he soon learned that that didn't work well for him.
He then discovered that more frequent and lower temperature saunas for about 10 minutes at a time worked so much better. He thought doing these more frequent shorter ones was much easier on the body, and was actually more effective. I think the principles of this are pretty similar to how I view more frequent, lower temperature castor oil packs (I do them almost daily). I've found them to be more relaxing and therapeutic than the hotter ones.
Also.... Edgar Cayce said castor oil packs have a unique ability to harmonize the sympathetic and parasympathetic nervous system in remarkable ways. I've noticed is that it feels so unusually calming and relaxing, that it provides a great time to do things like visualization techniques, meditations or contemplations, etc. If you'd be interested in some of the energetic techniques I do while doing a castor oil pack, I could say a bit more about that as well.