First, you should trim off leaves of the cauliflower and cut the heads into pieces about 1 inch across. You should then blanch the cauliflower by lowering them into boiling water or steam for 3- 4 minutes and then quickly cooling the cauliflower before freezing it. Blanching will destroy enzymes that will cause the cauliflower to deteriorate during storage.
After the cauliflower has been blanched, cooled, and drained, place them in a meal size, air tight, moisture proof container. Make sure you remove all air possible before sealing the container. Also try to allow headspace for expansion of the cauliflower during freezing. If you follow these steps you should be able to successfully freeze your cauliflower.