There is an art to bear-bagging.
First of all, you want a high branch. The food bags end up more than halfway down from the branch, so that still needs to be high enough that an upright bear can't reach them. For a rough estimate, assume that the upright bear can reach as high as an upright human reaching up.
The branch has to be substantial so that it will support the weight of the food bags plus the weight of a half-grown bear. Heavy adult bears can't climb much, but cubs and subadults climb well. The branch needs to taper out to where the rope is over it. That discourages the bear from walking out far enough on the branch to get the food. If the branch hangs down slightly, that is a plus. The branch has to be live wood for strength.
Some bears have been known to climb the trunk well above the branch, and then to jump out to try to score the food bags. That is what we call "kamikaze bears," and that is why some bears limp around the parks. If the bear successfully executes this move, the food hits the ground first, followed by the branch, followed by the bear. If you are camped right there, you have half of a chance to grab up the food bag and leave the bear out.
After the food is properly hung, I generally put up decoys to confuse the bear. These consist of empty paper bags tied with bright white cord, and they are tied about five feet off the ground. Noisemakers can be tied around the tree trunk. These consist of your cook pots and spoons, or anything that will clang together.
I led several group trips per summer in Yosemite, and this was back in the day before bear canisters were required. We always did the double rope technique, and never once did any bear score any of our group food. On one particular rainy night, our camp was the first one that the bears attacked, but they failed. The bears worked their way around the lake and hit all of the other campsites and scored food at each one. In the morning, we were the only ones with food, so we ended up sharing some of our food with the rest of the backpackers from around the lake.