Yes, there ARE rules. And the cans should come w/directions. Insulation is one BIG concern. They may be IC or not IC rated. Again, read the paperwork ...
RE: Where to put them, there should be 'coverage' info provided too. If the bulb is recessed vs. just the 'can' (but not the bulb), coverage varies. Again, read the paperwork. AT worst, talk to the Retailer that sold them to you.
My best to ya and hope this helps.
Jay J -Moderator