Judy,
First you have to have a complete understanding of each of the two decandling methods.
3 step: Divide the tree into three "zones". Strong, medium, and weak growth areas. (Actually 4 areas: add "really weak" zones. You don't decandle anything in the "really weak" zones.) Note that a single branch can have branchlets in each "zone".
Note: Determining the "zones" is used in both the 3 step and 1 step method.
Continuing the 3 step... decandle the weak zone. Cut the entire candle off at the base of the candle. Cut it straight across. Not angled. Leave a tiny collar. Don't cut back into old wood, if you do, you're cutting off the dormant adventitious buds you want to grow.
The weak zone candles are usually on the bottom of the tree, and/or candles growing near the trunk. Usually, the top of the tree is the strongest, so you would not expect to find weak buds up there. However, on highly refined trees, where interior backbudding is occurring, it's possible to find some weak buds even up in the crown.
Once you have decandled the weak buds, wait 10 days to 2 weeks and go back and repeat the process for the medium strength candles. Leave the strong ones.
Wait 10 days to 2 weeks, and go back and decandle the strong buds. Again, making sure to remove all the candle, but leaving a collar.
The idea behind the 3 step method is to give the weak buds longer to develop before fall arrives and the tree goes dormant. Your goal is to have all the needles be the same length at the end of the growing season. And have the bottom branches have the same apparent vigor as the crown. This is what we call a "balanced" tree. All the vigor (energy) is spread evenly across the tree.
1 Step Method:
This method uses the auxins already present to inhibit (delay) the development of the adventitious buds on the strong and medium branches, and allows us to do everything in one sitting. That way, you don't have to do each tree 3 times. The disadvantage is it leaves little stubs that should be removed somtime in the future. I do it as a part of fall work.
Divide the tree into zones as described above, and starting at the top, decandle the strong buds, and leave a bit of the stem. The auxins in the stem will remain active until the stem dries up. Which takes a couple of weeks. The longer the stem, the longer the auxins remain active. Be sure to remove all needles. Generally, only leave about 1/2 inch for the strong candles, about 1/4 inch for the mediums and only leave a collar for the weakest. Work down from the top. On those stems where there may be multiple candles growing from one spot, decandle them all. Again, leave the strongest longer, and the secondarys shorter.
Work your way down the tree, making sure to leave stubs consistant with the length you started with at the top. The terminal candles on a branch may be just as strong as candles in the crown. You want to leave the same amount of stub on those as you did in the crown.
To combine the two methods, you can do the 3 step, but instead of cutting them off completely at the collar, leave a little stub. Generally, you wouldn't do this on the weak candles, but you might on the mediums and strongs. You can vary the amount of stub you leave to be really precise so that you can give one branch (or secondary branch) more energy than another.
At Boon's we do the one step method. He has trees in all stages of development, including the most highly refined JBP I've ever seen. Based upon the results I've seen there, I'm going to stick with the one step method. Experience will teach you how much stub to leave to get the results you want.