The gravitational force between two objects is given by:
![force = \frac{GMm}{ {r}^(2) } \\](https://img.qammunity.org/2019/formulas/physics/high-school/p8m8hlh87ky9rr76nmintyyy0n73sop94g.png)
where M and m are masses of the objects and r is the distance between them.
Thus, the two things which can increase gravity between objects is:
1. Distance between the objects - decrease distance to increase gravity
2. Mass of object - increase mass to increase gravity