For pre-treating oily stains, try WD40's SpotShot. Think of it as WD40 without the fish oil. It works O.K. on new oil/tar stains, but older ones that have set in are a lost cause.
One of my biggest "pet pieves" are the stains from blacktop sealants that are used in commercial and residential parking lots or driveways. These get brought into carpets/floor mats on the bottom of shoes and are a REAL pain to get out, which I never seem to do sufficiently. Seems like they are ALWAYS present and the hotter the weather, the more they end up on said floor mats and carpets, discoloring them a dull yellow-brown . If someone has a surefire method of getting these out , I'd like to know what works.