I don't believe in past lives.

I think they are a waste of time.

Past lives imply an immortal personal soul. I find no evidence for such an entity.

So I have no idea how to read past lives.

The 12th House is "repressed contents." It is the personal unconscious. Anything unconscious will manifest as fate, and that is why the 12th house so often signifies unpleasant things. Things that hold us in bondage, or are self-defeating or self-destructive. Feelings of isolation or disconnectedness. Loss of touch with reality, confusion, unsettled conditions.

The 12th is also help from unexpected quarters, liberation from bondage, escape from pursuit.

Understand that all astrological symbols are univesal symbols. Each of them includes a plethora of meanings. First, their interpretation depends on the chart as a whole -- what they mean must be in accord with the significance of the whole chart. Second, you must "apply" the universal symbol to a "particular" question.

To read any house with no planet in it, look to the lord of the sign on the cusp.