David ,
This will come with experience and no doubt many experiments you trying different methods . Bare in mind the following
What type of oil is on the affected area ie petrol , diesel , hydraulic , ect
How long has the oil been down ?
Surface type ie, tarmac , blocked paved , concrete . resin ect Is the surface porous ?
Size of spillage ?
Disposing of contaminated waste ?
Chems , heat and pressure can assist but also can damage the surface !
Ed