If your brake pedal goes halfway to the floor before the brakes take hold, it is time to check the adjustment. The idea of adjusting the brakes is simply to move the brake shoes as near to the brake drums as possible without them rubbing, so when you push on the pedal, the shoes have the shortest possible distance to travel.
Jack up the car, starting with the right rear wheel (remember to block the left side of the car so it doesn't move). Pry off the hubcap and locate the hole near the wheel rim (in later vehicles you will find it on the inside of the wheel). Use a flashlight to locate the adjusting stars. Turn these stars gently, using a medium Flathead screwdriver through the hole, so the brake shoes move as close as possible to the drum and begin to tighten up on the drum. Then pry the star the other way one or two times to release the shoe so the drum can turn freely. You may hear scraping, but the drum must not bind anywhere. With both shoes adjusted, you can bleed the brakes and move on to the next wheel. Remember, any time you have the brake system open, always adjust and then bleed your brakes!