This is essentially the same process as freezing other veggies.  You just have to blanche it a little bit longer than the leafy greens.

• Put a pot of water on to boil, with a colander or steamer in it and with a top that fits tightly.
• Rinse the broccoli, then cut into florets and small pieces of stem
• Once the water is at a rolling boil, steam blanche the broccoli, covered, until they are uniformly bright green – approx 3-5 minutes.
• Rinse the broccoli under cold water to stop the cooking process.
• Spin the broccoli dry in a salad spinner, or roll it dry in a dishtowel.
• Put it into a plastic storage bag, close the bag nearly all the way, suck the remaining air out of the bag, and seal.
• Label the bag and stick it in the freezer to enjoy next winter!