The key to getting an amaryllis to rebloom is giving it enough sunshine during the growing season to regenerate the bloom(s). I generally put mine outside and give them morning sun and then in the early fall stop watering and let the foliage die off. Then you put them in the refrigerator and fool them into thinking they have been through a winter for approximately two months. Then you bring them out and repot and wa-laaa! Another amayllis bloom!
I have found out this summer that people in florida grow these year round and NEVER let them go dormant - but allow them to stay green year round and then they bloom naturally in the spring. I'm thinking of keeping them green this year and see what happens come spring - blooms? Will see!
Good luck on yours! mike