Cleaning can be done in two ways. First by using a cleaning agent(use WD40, or an alcohol-based agent), a soft cloth on the surface and dry off by cleaning using a dry cloth. Since it doesn't involve disassembling, stay away from the edges.
Second method: disassemble the trackpad and clean the edge of the hole where it fits on the laptop using a cleaning agent and a soft brush. Then clean the trackpad using a soft cloth or soft brush and clean its edge. Put your cleaning agent on cloths or brush not directly on trackpads.