There are a number of techniques which can be used to get grease out of clothing, as long as the clothing is washable and not made from delicate fibers. If the fabric must be dry cleaned, your dry cleaner may be able to get the grease stains out; explain the situation when you bring the clothing in and ask for suggestions. Delicate fibers can sometimes be treated for grease, although success is not guaranteed. In all cases, spot-test a degreasing solution on an area of the garment which will not be seen to check for colorfastness, as some cleaners can bleach or stain clothing.
One of the most effective ways to get grease out of clothing is to use a degreaser which has been specifically designed for this purpose. The laundry section of your market may carry some degreasers, most of which will need to be left on overnight to pre-treat the area before the clothing is washed. You can also check the auto parts aisle, as several companies make industrial degreasers for mechanics and other people who work with a lot of oil and grease, and many of these products are suitable for clothing. If you use an auto degreaser to get grease out of clothing, make sure to spot test it first!
You can also use dish detergent to get grease out of clothing. Look for a brand which is designed to cut through grease, like Dawn. Rub the detergent lightly into the grease stain to pretreat it, or simply run the clothing through the laundry with a few squirts of the dish detergent. Many massage therapists use dish detergents on their sheets to get rid of oil stains, as do restaurant workers and mechanics.
There are also a few more obscure tricks, which this Spiegato author has not personally tested. Baby powder is supposed to be effective if left on overnight, as are products like Goo-Gone, Goof Off, and Lestoil. Some people swear by Cheese Whiz, while others claim that a can of Coca Cola or Pepsi in the wash can remove grease stains. Shampoo has also been known to get grease out of clothing, especially shampoos designed for oily hair.
In all cases, you should wash greasy clothing separately from other clothing to avoid spreading the stain. This is also important when you have used something to pretreat the laundry, as the pretreatment may smell odd; many people wash greasy clothing once with the pretreatment and again on a regular cycle to get rid of the smell. You should also check the clothing to see if the grease stain has been removed before running it through the dryer, as the dryer can set the stain, making it impossible to remove.