Prove defamation. Prove that there was in fact defamatory language that reflects badly on your morality or integrity or questions your credibility in your profession. Historically plaintiffs aren't awarded as much for slander suits as libel suits, as written statements are believed to cause more harm than spoken ones.
Establish identification. Show that the slanderous statements in question were referring to you and be able to show that at least one reader could identify you as the one the statements defame.
Confirm broadcast. Prove that the public received--that they physically heard--the libelous statements in question.
Show fault. Prove negligence or recklessness, if not intent to defame, on the part of the defendant. You must show that the defendant was at fault for the broadcast statements.
Explain falsity. Show that the spoken statements were untrue. You only need to prove this in cases involving public concern.
Demonstrate personal or monetary harm. Show emotional distress or the loss of reputation or money. Annoyance is not enough for a slander suit.