1) Guard that number. Don't carry any document with your SS# on it in your wallet.
2) Protect your name. Get an unlisted phone #, or drop your address from the listing. Don't use titles in your listing (such as "Dr." or "Atty.").
3) Watch your mail. Pay attention to when your bills arrive each month. Big variances could mean someone is tampering with your mail.
4) Vary your passwords. Diversify your passwords, especially for financially-sensitive accounts (like online banking). Don't use "mother's maiden name" as a security question; it's pretty easy to get that information.
5) Check your status. Check your credit reports (all three) at least yearly. For privacy safeguards, stick with the major sites -- myfico.com, for example, or the sites of the three agencies themselves (Equifax, TransUnion, or Experian).