Washing up liquid always works for me when I get grease spots on my clothes, I don't know if it would work for larger areas though. I usually sqeeze a drop of it onto the stain, rub it in then put in the washing machine and wash as normal.
Using the correct dose of the best detergent would be a good start. Which? Best Buy "especially for greasy, oily stains" is Persil Bio Tablets - the non-bio version is also recommended, but not quite as good. And forget about washing at lower temperatures- you'll have to wash at the hottest that the clothes will allow.