As you might imagine, freestyle rapping can be filled with mistakes -- lines that don't rhyme, phrases or words that don't make sense, or lyrics you regret saying as soon as they exit your mouth. But that's part of the game and it's important to remember it happens to just about everybody who tries. The worst thing you can do after making a mistake is to pause and break what freestyle rappers call the "flow." If you just keep flowing, the audience will forget about the mistake soon enough. But if you stop, then the last thing they heard you say will define your performance. Even if you stumble through a line awkwardly, just keep going. Some skilled freestyle rappers actually use their mistakes and incorporate them into the next line to make it look like it was all part of the plan. You can also come up with filler phrases to throw in when you can't come up with something instantly -- "You know what I'm sayin'?" can even buy you a few seconds to regroup.
Always think ahead. When you let loose with a line, think about the word you are going to have to rhyme. If you know the next line you are going to speak ends with "game," start thinking about rhyming words. With practice, you will develop this skill and know within a second or two that you could use "shame," "lame," or "tame." You will have to develop your brain's ability to multitask.
Don't worry about making your freestyle sound too polished. If it does, then the audience will assume you're cheating. They'll think you wrote it all down ahead of time and memorized the lines. This is a no-no in the freestyle rap scene. The whole idea is to show you can come up with rhymes on the spot and without preparation. If you are wondering how to prove you are truly freestyling, try to incorporate material using what you see around you. A line about an object in the room, a girl in the crowd, or what the other rapper is wearing will win over a crowd much more than a generic line about something you did yesterday.
While you can't write and memorize your freestyle rap lyrics, you can write rhymes every day -- and you should. Write rhymes daily about current events or local happenings. You may not use them in your freestyle session, but you can bet the words you used to rhyme and the topical information will make its way into your act.