Well, part of the answer is going to depend on what kind of Furcraea it is, but they do have some things in common. In the ground, let the top 10-15 cm of the soil dry out between waterings. In pots, let the top 3 cm dry out. The thicker the leaf in proportion to it's width, the longer it can go without water. Most of the wider-leaved species like a little afternoon shade. The ones with narrower leaves and bigger spines can take full sun. They don't need much food, but something like rose food once or twice a year in the ground, or once a month in containers, will help keep them growing and well colored. Further info if you can ask again with more particulars.