In the old times, geostationary satellites had their longitude windows, each with around 1°, and tried to keep themselves at the center os this window. This strategy was good enough for its time, when few satellites with poor attitude controls were located in this orbit.
Nowadays, geostationary spacecraft are usually in a "collocation window", which is based on the windows of the past, but now more than one satellite is located at the same window. The basic technique to ensure two satellites are far from colliding is the eccentricity-inclination vector separation.
Basically, this technique gives a mathematical condition to impose for a modified set of elements, where each participant operator in the collocation window keeps the eccentricity vector and inclination vector in a circle around a nominal value.
Operators still need coordination with regards to RF interference and procedures for collision avoidance maneuvers against dead satellites or debris. Luckily, these objects stabilise at a few degrees of inclination, hence they only pose a treat twice a year.