Unlike in English, adverbials in German do not command certain tenses or tense relations. Rather than that, you have to understand the adverbials in the context of the tenses.
Especially, the tenses move the viewpoint.
Bevor ich schlafen gehe, lese ich ein Buch.
That's either a timeless statement or you mark both as certain to happen. In that case, the viewpoint is now, and both things happen in the future. In that order that is hinted by the adverbial.
Bevor ich schlafen gehe, habe ich ein Buch gelesen.
This only makes sense if the viewpoint is moved to the future. That action of reading the book has already happened, but not the action of going to sleep. It's still told from the position of now but it demands the listener to move their viewpoint inbetween the two actions.
Bevor ich schlafen gegangen bin, habe ich ein Buch gelesen.
It this example the viewpoint is moved even further into the future. So far that both actions are in the past.
Bevor ich schlafen gegangen bin, hatte ich ein Buch gelesen.
Again, the viewpoint is in the far future but the order of events is
emphazised. This form is not too common.
Bevor ich schlafen ging, hatte ich ein Buch gelesen.
This form is slightly different as Präteritum marks this as storytelling. So the viewpoint is from outside of the story into it, and again, the order of events is emphasized.
Bevor ich schlafen ging, las ich ein Buch.
Again, Präteritum marks this as storytelling but the order of events has to be guessed from context — from the adverbial.