Well, I'm new to producing videos, I only have one so far, but I'll share my little knowledge with you:
By the way, this is my music video: https://www.youtube.com/watch?v=dq7nUScFtes
1. Download, I mean buy adobe premiere and after effects (of course you can use other programs, but this is what I use). Take your time to sit through all the basic tutorials, and then some more.
2. Once you understand how the programs work you can start gathering footage (or recording).
3. If you want to put together a music video using footage recorded by other people start browsing on youtube, saving every single clip that looks good. Arrange your stuff, you might end up with hundreds of videos.
4. Download those videos.
5. Put them together in premiere. On the audio channel there should be your song, so you can edit your footage to fit to your song.
6. Export that, then you can apply some really cool effects in adobe after effects.
What effects should you use? Anything you want. It is a witch house video, it doesn't have to look good. You can fuck with the colors all you want, you can compress the video image until you can barely see what's going on. You can record the whole thing with an old vhs cam. You can export the video, play it on an old crt monitor and record it with your camera. You can fill your video with errors and intentional glitches and shitty gifs and all that. If your music sounds dirty your video should look dirty too. Whatever weird, fucked up idea you have, make it happen.
The key is to really make it, because nobody will like a video that only exists in your head.
Oh, and we don't really have much witch house music videos, so we should really get our shit together. There are so many possibilities.