Is there anything of a best practices on how to use your own modules?

I've been doing a LOT of this in perl and have just started to play with it in Ruby.

Some things I am transistioning from are:
use lib -- how do I specify an alternate location for files?

modules/object/files:
It may be bad form to put more than on class in a single file, I know it is in 
Perl.  But is there a reason not to?  I have some classes that are very tightly 
related in inheritance and they are very small.  I don't see much advantage to 
ever physically breaking them apart.