It works quite nicely on Facebook. It goes like this:
Friend: Had a bagel with cream cheese for breakfast. NOM!
Me: HAHA, VERY FUNNY! April fool's right?! YOU GOT ME! Good one!
The secret is to pick something that in no way, at all, could be meant as an April fool's joke. Something bland and innocuous and tada, instant hilarity!
Note-This is not appropriate for announcements of deaths, really. My family, thankfully, was wise enough to hold off on telling us that my grandma died last year on April 1st, because they are all a bunch of jokers (hence why I am probably averse to being tricked) and I totally wouldn't have believed them.