My husband was a truck driver for 16 years, so I know about grease stains!! What worked best for me: If the grease is fresh, then I used an Oxy type powder and would make a paste to put directly on the stain. It seems to work well with out leaving a spot. If the stain was older, then I used a kitchen type grease cleaner. I was water it down a bit to make sure it wouldn't discolor the item, then spray it on, let it soak in then wash as usual. Sometimes the best solution was to just trash it, depending on how bad it was. Good Luck!
You can do it the old fashion way and take a bar of soap and rub at the grease spot. If that doesn't work there are specially made spot and stain removers you can purchase at your local grocery store and or market.
Dawn dishwashing liquid -- best grease fighter out there. Sometimes it needs 2-3 tries, depending on how much oil/grease is in the stain (I have a habit of splashing olive oil on myself -- I have lots of practice).