I need to start carrying a tape recorder to chronicle my ranting and raving-which I am getting better at, a lot better. I find there are 3 ingredients to a good rant.
1) A good rant needs to be the culmination of stuff you have already been thinking about for a few days. In other words your rant needs to marinate.
2) Alcohol.
Its important not to fear consequences when you are ready to bring the heat. You can't allow yourself to stumble over or try to pussy foot around a sexist or racist word. Its also important not to be self conscious or even self aware while executing a good rant. Furthermore the booze allows you to deny responsibility the next day.
3) Mental Instability.
If you are going through some emotional hardships, that can help to push your rant over the top and distinguish you from other people who are simply whining or trying to be funny. Harnessing your self hate and feelings of inferiority can give you that crazy sparkle in your eye that makes your audience afraid to stop listening to you-better yet they are almost too uncomfortable to even laugh! Channeling your inner crazy will also help you avoid predictable punchlines and keep people guessing.