Prepare a sample of liquid to be tested in a large receptacle, such that you have enough surface area to the probe of your instrument. Common probes are the Du Nouy ring and the Wilhelmy plate, depending on the force tensiometer. Some instruments use smaller metal rods, which are better suited for smaller sample sizes that have less surface area.
Adjust the force to zero when the probe is above the liquid surface. This insures the force measured during the experiment is as accurate as possible.
Lower the probe slowly into the liquid, through the surface layer. Once through manipulate the force tensiometer to raise the probe slowly out of the liquid. As the probe is raised through the surface layer, it will be resisted by the cohesive forces of the molecules and exert a force on the tensiometer. This force will increase to a maximum until the bond with the surface area is broken as the probe is removed completely from the liquid.
Make note of the force applied to the probe by the liquid sample. Many instruments will have data capturing abilities and will provide a graph to show the force through all aspects of the experimental procedure.