Your poinsettia is finished blooming for this season. You can trim off the red bracts, and re-pot as Daisy suggested then let it grow outside for the summer with a little fertilizer and regular, (not too much) water. If your lawn is on a sprinkler system, say twice a week, that much would probably do fine for it. They like hot, dry weather but be sure you don't let the pot get too dessicated.
In the fall, you need to bring it in, somewhere it will get the right light/dark cycle, I think it's @ 12 hours of each, so it will set some more blooms and be beautiful again. Even artificial light such as street lights or lights in your house will throw off the bloom set. This is the reason it's such a difficult thing to get them to re-bloom. Yet, you see them growing by the roadside in Mexico (where they came from) and blooming 10ft. tall with bracts 18in. across with no care whatsoever, so it's just a matter of getting lucky and supplying the right conditions.