Get into your zone. This means different things to different people; some may like to hype themselves up before while others prefer to focus intently on the situation to come. Whatever you have to do to mentally and emotionally, prepare yourself in order to be comfortable and to think clearly.
As soon as you find out who your opposition is, study her, characterize her and pick out points of weakness you may see. If your opponent raps before you, use the time to formulate a response to her rap. This will give you more options and ideas when your performance time comes.
Formulate a plan of attack. Begin to work out rhyme sets in your head that you can use. Start making the first line in your mind and use the other brainstormed ideas as a "cue card' to spark your ideas when rapping. Basically, think or what you are going to say and how you are going to say it, but leave yourself open to inspiration. The trick is to find and effective balance between preparation and spontaneity.
Spit flame. Capture the heat of the moment with your words and allow them to come out of your mouth methodically to the beat, if there is one, when it is your turn. Make sure that you keep tempo even if you are doing this a capella. Try to rhyme at the end of stanzas, changing the rhyming sound when you feel comfortable.
Alternate turns freestyling. Depending on the rules of your event, you may or may not alternate several times back and forth with an opponent. Remain focused and try not to let your opposition frustrate you to the point where you can't think of a come back.
Declare a victor. Most of the time, spectators or the participants themselves will declare a winner based on the performance. Things to keep in mind when determining the winner are lyrical content, delivery, performance, attitude, style and endurance. Other dynamics may be taken into consideration as well during a freestyle battle event.