For a planet to be habitable, there has to be an energy source to sustain metabolism. The planet also needs to have mass and luminosity as well as orbital and rotational characteristics. This means that the planet should be able to rotate at a relatively fast pace so as to balance the day and night cycle. Visit http://en.wikipedia.org/wiki/Planetary_habitability for more information.
That would depend on what is going to live there. If you are asking what it would take for humans to live there, it would take oxygen, water, soil to grow plants in, temperatures in a livable range, a sun near enough to provide light, and a weather system that is not too violent nor too calm.
But, even on Earth there are creatures that can survive where humans can not.