I usually pot the tubers up around early April, in 6" pots and put under grow lights in the basement. I have grown them without the lights but they tend to get really leggy by the time they are ready to go outside. The ones that do best in my garden are in light soil (I've planted extras in heavy clay and they never grew well).

You need to harden them off like any other plants that were started inside. Give some thought to where they are placed in the garden...make sure they aren't too shaded by other plants. You'll get earlier blooms with short varieties rather than, say, the large dinner plate ones, which need to get to a fair size before they will bloom.