Private vs. Common Carriage is a must. Know the systems of your A/C as well as that of a commercial A/C ( IE Air Conditioning/Press. Ops, Turbocharged Engines, GEAR SYSTEM/HYDRAULIC- Know how to draw/explain these !! ) Most of all just relax and try try try not to start every sentence with Ah's and Um's and ' Well Basically '. Instructors here this all the time and they're just space fillers and make you sound less educated than we all know/hope you are !