Doing these drills once or twice isn't enough. Continue to practice and apply what you've learned out on the road.
In my experience, most cyclists take handling skills for granted. Consequently, a lot of crashes can be avoided by being aware of your surroundings and having the skills necessary to react instinctively to emergency situations. By practicing these skills in a controlled environment, you'll become a faster and safer cyclist.
To get started, find an open area where there's no traffic (like a parking lot), some orange cones (water bottles can be substituted) and a partner.
Braking: Begin circling the course. Have your partner randomly call out "stop." Bring your bike to a quick, safe, controlled stop. Have your partner stop quickly as well and look at the distance between your bikes. If you have good reflexes and reaction time, the distance between your bikes will be close.
Practice braking in a variety of situations, such as cornering and braking with your partner in front of you (be careful). If you're a beginner, apply both brakes with even pressure. As you get more experienced, apply slightly more pressure to your front brake.
Cornering: Choose your line through each corner. If you corner correctly, you should clip the apex of the turn. Make sure your inside crank arm is in the vertical position so that your pedal doesn't touch the ground. Practice cornering inside and outside in both directions and try to pick up your speed each time. Start to sprint out of corners. Set up a slalom course and also practice 180-degree turns.
Looking: A key element of road safety is being able to see what's going on around you. Beginners have a tough time looking over their shoulder while keeping their bike straight. Have your partner ride several bike lengths behind you. At regular intervals look over your shoulder and call out how many fingers your partner is holding up. Have your partner tell you if you veered or continued straight.
Bumping: This needs to be performed on a grassy field using a mountain bike. Have your partner "bump" you slightly and touch shoulders simulating situations that occur in pack racing. You should get used to contact with other riders without panicking.
Riding position: Practice transitioning smoothly from various riding positions such as sprinting, climbing in and out of the saddle and descending.
Drafting: Have your partner vary his or her speed over the course and try to maintain a constant distance from you partner's rear wheel.
Performing these drills a few times per season won't help you much. You have to take what you learn and apply it on the road. Good habits need to be practiced thousands of times before they become good form.
Awareness is your greatest asset when riding in traffic situations. Try to anticipate what drivers are going to do. Eye contact is very important, as is visibility. Constantly check what's going on around you and stay focused on what you're doing.