Answer:
Scientifically speaking that's a very broad question, and can depend on the actual planet itself. But perhaps I can answer your question with another question.
Earth has life on it....? What are the requirements for life on earth? What does an animal, plant, or microbe need to survive?
That answer is simple:
1. Water - All life on earth requires water.
2. Food - All life on earth requires food to survive, whether that's a plant that makes it's own food through photosynthesis, or an animal that hunts for its food, or a bacteria that feeds on the waste of other animals.
3. Reproduction - In order for any species to continue to survive, it must be able to reproduce.
Those are the basic requirements of life.