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Grab a pen and paper, or print out some storyboards from the internet. A storyboard is simply a comic-book version of your video, which allows you play with the shots and ideas without wasting time or money on set. Remember that a story, at minimum, needs three parts, which you can diagram or illustrate any way you want. For an example, check out the humorous story in Das Racist's "Girl," which almost anyone could shoot on a minimal budget:  The Problem: First, we meet the characters -- a gorgeous girl and a working class boy who is immediately in love with her. She doesn't notice him. The Struggle: Second, we realize the boy doesn't have the courage to talk to her, so he follows her instead. Using purely visual jokes, the video explores his increasingly funny attempts to get close to her. The Resolution: He gets beaten up for his love by some thugs, but he doesn't give up. In a hilarious reversal of expectation, he makes his move finally -- on Facebook. Note how this is only about 50% of the video -- your story doesn't have to be long, as rapping and dancing can fill up the rest of the time. Use the cameras to find your angles for each location, then set the actors up in a "dry run." Once you know where they'll be and where they need to move you can set lights to ensure everything is visible and well-lit. In general, your goal when lighting is to have a few deep, dark blacks, small sections with clear whites, and a large range of grays and other colors in between.  The 1-2 hours before sunset and after sunrise have the best lighting of the day. Overcast days, however, are the most useful, since the light is calm but widespread under the clouds. While three lights with even shadows are the norm, don't discount more adventurous lighting patterns, like Coolio's "Gangster's Paradise," which uses interrogation-type lighting for a extra dramatic feel. It can help to prep shots in black and white mode to see how the lighting looks without color. A good shot in black and white will look great in color, usually. This isn't a feature film requiring precise, coordinated movements. Let people have fun and keep your direction simple. In general, you'll have the best results by letting people bring their own personality on camera instead of micromanaging. If you're in with friends or trusted collaborators, consider having someone "in charge" of the extras, providing light instruction while you set up shots or lights. If something happens to your production you want to be sure you have enough footage for a full video as soon as possible. Pick your favorite 1-2 locations and run through the whole song several times, ensuring you could put a video together even you can't film again for some reason. Take multiple angles here instead of shooting the same shot three times. If you know the first one is good, move the camera before doing it again. Rap is a personality-driven art form, where the individual rapper is the main force behind albums, videos, and sales. Make sure that they are the focus of all the rapping sections, and they don't leave the video for too long during any one section. Good ways to keep them involved but still have an interesting, changing video include:  Costume or outfit changes. Rapping while "in action" (driving, counting money, flirting, etc.) Using extreme or interesting angles, like very low/high shots, fisheye lenses, etc. Because you don't need to sync dancing or rapping with the story shots and there are no lines of dialogue or microphones to set up, you can usually "run and gun" story shots quickly once the main shots are finished. When shooting story shots:  Keep a checklist of the shots you need and cross them off as you work -- nothing is worse than getting into editing and realizing a key "chapter" is missing. Take 2-3 takes of each shot, ensuring at least one of each will work. Keep the shots short -- think of linking a lot of little images instead of filming one continuous story. B-roll shots are images that you don't have a place for yet, but will eventually fill in any gaps you have while editing. Think of a feature film, where many scenes start and end with artistic shots that aren't strictly necessary, but tie the whole thing together. Some ideas of B-roll include:  Solo or up-close shots of important props. Shots of the dancers or extras having fun. Cool shots of each location, helping the viewer see where you are.
Diagram any story shots in advance. Stage each scene with actors/rappers/extras, then set up lights accordingly. Keep your direction simple and loose, especially with extras. Shoot 2-3 takes with the song playing and rapper rapping first. Make sure the rapper is the focus of most shots. Grab any story shots without sound to speed up the process. Pick up B-roll, or extra shots that look cool, in the end.