1.Disable Flash on everything but youtube(or anything you deem safe)
2. Disable or delete Java.
3. Don't download cracked programs OR download only those older than 2012 or older.
4. Don't store your wallet on Dropbox.

Follow above steps, and you don't even need to run an anti-virus, which is btw, recommended. You can thank me when your 1btc you kept safe is worth $100k.