Whenever my boyfriend degreases our car engine he always manages to get stains on his clothes.
So, my best tip for engine degreasing would be to use very old clothes while you're doing it, and to try not to touch them. Get some of that really harsh pink pumice soap that farmers use, to help clean off your hands afterwards.
And if you do get grease on some clothes and want to try and save them get a commercial product to do it. There are lots of so called grease remedies online, but I've found only the ones from the supermarket really work!