1. DON'T half-ass it. Put some effort into it. This is the one day of the year where you can playfully take some aggression out on your friends and coworkers and really let your pettiness shine.
2. DON'T give it up on it too soon. If your "target" believes whatever insane story you're telling them, don't yell "April Fools!" right away.Let them sweat. It'll make the reveal so much sweeter.
3. DO play nice. You're not looking to ruin anyone's career, relationship, property, or life. This is supposed to be fun you jerk.
4. DON'T tempt fate. Call it superstition, but pretending that someone died or that you're pregnant should always be off the table.
From ChicagoTribune.com - The Second City: April Fools’ Day do’s and don’ts