* The masses of the objects are larger: The more massive the objects, the stronger the gravitational pull between them. This is why the Earth pulls you down, but you don't pull the Earth up with the same force.

* The distance between the objects is smaller: The closer the objects are to each other, the stronger the gravitational force. This is why you feel the Earth's gravity much more strongly when you're standing on its surface than when you're in orbit.

Here's a simple way to think about it:

Imagine two magnets. The closer you bring them together, the stronger the magnetic force between them. The same principle applies to gravity. The more massive the objects and the closer they are, the stronger the pull.