I realize this is a very basic explanation, and I think it is good for the beginner. The only things I would have to say are either based on your supplied technique. So, I will point out the things that I think could be improved on. I notice you didn't mention how to store cuttings, since this is about rooting cuttings, but I want to add some feedback about refrigerator storage also.
You mention using a Zip-loc baggie and left it at that. Dan always jumps on people about this (in a nice way, of course) - he says you should note what kind of Zip-loc baggie - "freezer" or "storage". Dan recommends "freezer" bags for storing in the refrigerator and "storage" bags for trying to root. There is supposedly a difference between the two. I tend to agree.
During rooting, I personally roll my twigs into a bundle with the bottom of the stick exposed so I could see the roots/initials forming. I believe Dan recommends that you simply place a damp paper towel into the bag and do NOT wrap it around the twigs. I like your method, but it doesn't show me the roots without removing the cuttings from the baggie, which leads to contamination, thus potential mold introduction. To get the proper dampness most people recommend, I found that folding the paper towel in half several times, soaking it, then wringing it out completely will give you the correct moisture level. The spray bottle is something I've never seen, but it's a nice idea. I would recommend trying either to folks.
When storing my cuttings in the fridge for later rooting, I prefer to bundle them up and wrap with Saran wrap (plastic wrap) around the bundle, Leon's method. I place in a freezer bag. I like this also because I can write the cutting name on the plastic wrap using a Sharpie marker, and not worry about it bleeding away. This lets me put multiple cuttings in one big bag. It does no damage to the cuttings.
I realize this is not part of "simple" baggie methodology, but you didn't mention cleaning the cuttings, which can help with mold and rot. First lightly scrubbing with anti-bacterial soap and a toothbrush, then dipping in 10% diluted bleach solution, then air-drying and placing into the baggie both a) prior to storing in the fridge and b) before setting up the .
Finally, for humidity, when suggesting inserting direct into soil, you can maintain good humidity and more constant temperature for rooting by placing a bag over the top of the pot OR maybe a soda bottle with the bottom cut off and cap still on loosely.
Also, Celsius degrees only? ;)