In order to save your printquota, you should print more than one logical page per physical page
wherever possible. This is particularly easy to do with lecture slides which have lots of white
space surrounding the text, and which are usually designed to be printed multiply.
The basic command is mlpr. It has many options (type man mlpr for all of them) but the most immediately useful are:
-2, -4. -8: 2, 4 or 8 logical pages per physical page
-L, -P: landscape or portrait orientation (portrait is default)
+d: don't print dividing lines between the logical pages (dividing lines are default).
So to print 4 lecture slides on each side type mlpr -L -4 -P<printer> <file>.