Methods for preparing a metallocene-based catalyst composition that can impact the long chain branching of ethylene homopolymers and copolymers produced using the catalyst composition are described. The catalyst composition can be prepared by contacting a metallocene compound, a hydrocarbon solvent, and a first organoaluminum compound for a first period of time to form a metallocene solution, and then contacting the metallocene solution with an activator-support and a second organoaluminum compound for a second period of time to form the catalyst composition.