Photo: by Bryan Costin (flickr)
If you garden in a cold region, by now you should have brought in your pots of amaryllis that summered outdoors. They need to be now in a cool, dark spot where they will not freeze as fall temperatures drop, so that they can go dormant. They need at least 6 weeks of dormancy, without water or light, and all of the top growth needs to die back and go brown. Remove the dead leaves and start watering them again and bring them into a light area, when you are ready to start them on their way to re-blooming in the house.
Gladioli and dahlia bulbs also need to be dug in the fall and stored in a cool, dark spot in peat moss or in brown paper bags. Cannas are very forgiving and can be dug in clumps and the tops cut back and put en masse into black plastic bags for the winter. Storage at temperatures of 40-50 degrees F. is best, so basements and cellars are ideal for all warm weather loving bulbs.
All tropical plants must be kept from freezing, of course, and stored in a state of dormancy. Lack of warmth inhibits growth, which is why cool temperatures are best. Fertilize tropicals during the summer when they are growing normally.
Coleus plants, and other tender annuals like them, can be carried over as cuttings. Strip off the lower leaves of these cuttings and keep them in a glass container (so that you can monitor the water level) on a bright window sill, or cut back a container plant hard and keep it under lights for the winter. By spring, the cuttings will have formed a mass of roots which can be gently untangled, and the cuttings can be potted up and the new plants can grow (and be pinched back to make them bushy) for eventual spring planting outdoors when all danger of frost is past.