I have just finished recording a series of songs for a Progressive Rock/Metal Musical.
In writing, I was careful to structure the songs, so they did not rely too heavily on visuals,
giving me more freedom during filming.

I have never filmed a music video, or anything that required lip syncing.
Are there any techniques or methods that could help me? Any sort of advice would be helpful :)

Well, first of all maybe you should tell the band (if there is a band on stage) to actually play live during the shooting process. I guess it can make the video more natural and spontaneous. It's not so easy to make a good lip sync.