Grease can be very difficult to get out of clothing. The most important thing is to treat it as soon as possible. Try a little bit of Dawn dish soap, just put it directly on the grease and let it pre treat, then wash it. You can also try a product called Bix, it works great.
To get grease out of clothes try a commercial pretreater liquid. If this does not work my husband uses WD40. Spray it on the clothes and then wash. Always test the fabric first before using any new treatment.