Very hot water worked for me too. I would run hot water on my hands; water that would be too hot to get into. It would feel so good. Oh, it feels so good. It only takes a minute and then the itch is gone for about 12 hours. It is difficult or impossible to do for some areas of the body but for those people that get it in the future, if you can run hot water on it, that should work great. Do that instead of scratching. I now have something else on my skin; probably psoriasis and hot water works for it too.
The best thing to do is to know what the plant looks like and avoid it. If you are exposed, take a shower as soon as possible, as others have said. Strip off your clothes carefully to attempt to avoid contact with clothes if possible. Wash the clothes immediately.
I have cleared out Poison Oak and as a result had intense close contact. So I am experienced.