Planting a blue agave cactus?

I bought a good sized blue agave today for $80 and have never had one before. I understand they dont need much water, since i'm in humid Houston TX, only to water once a month. How about planting them? I understand I need to put it on a high spot to allow the water to drain off, and put rock underneath it and around it for drainage? Any other advice? What about fertilizer? I couldn't find much info on the web for these things.