If you boil them for more than a few seconds, you'll start cooking the tomato, which can make it harder to work with -- you effectively want to cook just the bit under the skin, which only takes a few seconds.
I work with a paring knife and a set of spring loaded tongs (but you could use a spider or strainer).
- start a pot of water boiling
- cut an X in the bottom of the tomatoes
- once the pot of water is boiling, reduce to a simmer
- drop a tomato in the water for about 5 seconds.
- let the tomato cool for a few seconds. (you could use cold water, I just wait).
- hold the tomato in your off (non-dominant) hand
- hold the paring knife in your right, but not for cutting ... grab it like you'd hold a paint brush, with the tip of the knife blade near the end of your thumb, and your thumb against the flat side of the blade, and the sharp side facing towards your body. (this is one of those cases where pictures would help).
- slide the knife under one of the 4 flaps left from the X, grab the skin with your thumb and pull.
- repeat for the other 3 flaps.
- if there's any skin left, repeat until the tomato is clean.
If the skin was still sticking, increase the time for a second or two until you find the right time. If the tomato was getting difficult to hold, decrease the time.
Once you find the right time to cook the tomatoes for, I cook about 3 romas or two larger globe tomatoes at a time -- while one batch is cooling, I peel the previous batch, dip another set, repeat, and you'll have a batch done in no time.