from National Geographic:
Earth is well equipped as a planet and ideally placed in our solar system and galaxy to support life as we know it. The product of some 4.6 billion years of cosmic construction, our planet is flush with life thanks to a fortuitous set of conditions.
1. Our location is far from many hazards
2. Our sun is a stable and long-lasting star
3. We're at just the right distance from the sun.
4. We have to right stuff to host a dynamic core.
5. We have a big moon to stabilize our axial wobble
6. We have an ozone layer to block harmful rays.
The details of each can be read here.