1.) I'm not the biggest fan of game footage since I never have played the games that most game amv's come from. All I know is I see too many Final Fantasy videos.
2.) I say go for instrumental music. Its not used much (as far as I know) and can make some incredibly powerful music videos. I realized this since I am part of the Instrumental AMV project. Thanks for rose4emily for showing me a glorious thing!
3.) Using the voices or clips from the anime's episodes/movies is something I wish people would do more since it can add a very interesting and more personal feeling to the video. To me it can emphasize the story the song and the anime is conveying.
4.) I wouldn't recommend using original art or animation unless you are uber good at it. Of course it might be useful for making a comedy video or something.
5.) On effects I think they are good as long as the footage is still visible (ie not blured and colored out, or so many transitions it makes your head spin) and doesn't cause seizures ^_^! I've also found it a good idea to mess around with the effects settings if they have any. Most of the time the default settings aren't the best choice. It all depends on what you are trying to create.
But the best way to make a video is to just go out and do it. Spend a week trying multiple ways and styles. I never really plan a video out, it just sort of comes to me all of the sudden or while I'm editing some footage randomly
! Have fun while doing it too
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