The gravitational force between two objects increases as

Their masses increases or the distance between them decreases

Explanation:

According to Newton's law of Gravitation, the gravitational force exerted between two bodies of masses and  and separated by a distance  is equal to the product of their masses and inversely proportional to the square of the distance:

  (1)

Where is the Gravitational Constant

As we can see, if one body increases its mass or if both bodies increase their mass, the gravitational force will increase as well.

In addition, is the distance between the two bodies is decreased, the  gravitational force will increase.

Therefore:

The gravitational force between two objects increases as their mass increases or the distance between them decreases.