What is the best way to double expose a photograph?

I’m curious about double exposure.

Like, should one under expose both shots? Or is that unnecessary?

Is there a particular film that is best for it? (I have 664 Polaroid film in mind for a 100 Land camera.)

What are some thoughts about composition when double exposing? Juxtaposition, congruency, ect…

Do double exposure photos appeal to you? What are your thoughts on this type of picture?

Any other info about this subject would be much appreciated! :)