The answers to your questions demand very long and detailed answers, as you're almost requesting an explanation on how to direct a music video. There is no specific answer to the question of "how to direct a music video", however here a few tips from an experienced music video director (me), which are some of the things I do on most jobs.
It all starts with a "treatment", which is a brief description of what you want to achieve in terms of a concept or visual for the music video. This can be narrative, or performance-based. Let's assume you've decided to go with a performance-based concept, which a lot of the time has nothing to do with lyrics or what the songs "message" may be. It can simply be a video of the artists performing against an infinite white backdrop with props incorporated within the different "vignettes" such as their instruments, a car (common with hip hop videos), or objects that are used in the background to enhance the visual according to what's being said in the lyrics.
After the concept is worked out and you're going to camera on the video, you've planned out your shoot day in terms of what you need to cover by way of a shot list usually, and if the budget allows you can also have a storyboard (though unnecessary for most performance-based videos). We refer to each different performance shot or "scene" as a "performance vignette" at our production company (and almost industry-wide here). Each vignette where sync to playback is required is shot usually on 3 different lenses for coverage and the artists usually play along and mime to playback music played off of some kind of sound system. Some vignettes are shot with the entire song playing, and some are shot with portions of the song depending on where those vignettes fit into the concept (sometimes depends on outfit changes, location changes of which may appear later in the video according to the concept, etc.) Finally, once all main vignettes are shot for a performance-based video, we then move into filming our "pickups". These are shots that are shot sometimes at the end, or sometimes during the main vignettes, or wherever they are needed (no rules here), and are basically shots that can be anything you want either for the concept or as filler. Examples include close-up beauty shots of fingers on a fret board, the singers mouth lipping lyrics, various high-speed shots such as a guitar being smashed or an artist giving a stare into the camera, swinging a mic by it's cable, and the list goes on and on and on).
Key things you might want to consider in production, and especially post-production (specifically the edit) is pacing and how fast cuts are and how they are placed, as well as what is seen when as the video progresses in terms of visuals. You want to try not to get too repetitive with pickups and cuts. You want to also make you or your editor is considering cutting on beats if that works for the video.
In a nutshell, that's what it is. After all is said and done, it all depends on the concept and how it's covered and shot the day of the shoot. Since this is just for a friend, it's a great opportunity to see if you have what it takes to direct a music video.
Anyway, good luck to you!