Use a mannequin head and place it next to your partner while they sleep. Wake them up and as they try to look at you they freak out as they see the fake head.

This prank is one to build up to April Fools Day. Every time you are near someone leave pennies / small coins without them noticing.

This one is great to prank your colleagues who work on a computer during April Fools' Day. Switch their computer screen upside down during a break.