+1 Don't use your rear brake. When I was a noob, riding my MTB, I would always use the rear brake because I had no modulation abilities. Recently, I learned how to modulate with my old hybrid and when I got my roadie, I transferred that skillset and now I can stop on a dime. The sweet spot is getting it so your rear wheel is just before the point where it lifts off the ground.
Just be careful not to pull it too hard in a panic stop. The other day, I was coming down a small hill on the local MUP at about 25mph. There was a jogger on my right and a jogger on my far left (right side of the oncoming lane). A couple of cyclists were trying to pass the jogger in the oncoming lane, coming towards me. Of course, there was only enough space for me to go through and I was travelling much faster than them, so they should have let me go through without any problems. Then one of them decides to turn into my space and I almost hit him. I hit on the front brake and decelerated to about 10mph in about 75ft. I got it to the point just before the rear wheel lifted above the ground. This should be a good example for how good modulation with the front brake is much more effective than locking your rear wheel.