Measure the space between the shower walls where you intend to install the curtain rod. Typical shower curtain tension rods come in varying sizes ranging from 36-inch lengths to 72-inch lengths. The diameter of tension rods varies from 3/4 inch to 2 inches.
Adjust the rod to fit your space. Place one end against the wall in the desired position, and pull the other end apart until it reaches the adjacent wall. Push the rod into the walls until it won't move anymore, and twist the rod to hold it in place.
Adhere to weight limits. Check the package for the manufacturer's recommended weight limits. Tension curtain rods are typically not able to withstand more weight than a curtain and a towel or two at any one time.