So, calling in sick when you just want a day off is a pretty old trick, but it still seems to work, if you're not an idiot.
Pretty much people make the same mistakes that get them caught when they call in sick.
-Don't make a fake sick voice - I mean really, c'mon. We know you're faking, no one really sounds like that.
-Call at the right time - Calling the night before is a bad idea, you're going to wait until you're sure you are still sick the next day. Calling right before you're supposed to arrive is a bad idea too. You know well in advance that you don't feel well. Calling right before is like saying, "Hey, I don't want to work today, and I just decided that, so I'm, uh, sick...."
-If you're really looking to sell the thing, try faking some symptoms the day before - Don't be overt, but if you can get the idea into the bosses head that you're coming down with something, he/she will connect the dots the next day when you make the call.
-Don't have any evidence of any activities other than bed resting and movie watching - going to the pool or beach is a bad idea when you call in sick. When you show up to work the next looking like that kid in the picture above, your cover is blown.