Just type ``echo $PRINTER'' and hit return.
Type setprinter printer-name and hit return.
You need to tell the application you are using which printer you wish to use. Each printer has a name, and multi-function printers have names for each function. For example, the heavy duty printer in room 438 is called mx and for double-sided 8.5 by 11 paper it is mxd. For most applications your just add the printer name, prefixed by -P to the command. Assuming you want mxd, the following examples will do it.
For Netscape, acroread (for .pdf files), and others where pressing the print button gives a window with the print command lpr just add -Pmxd, so the window shows lpr -Pmxd.
For printing dvi files created by TEXor LATEX, dvips -Pmxd filename.
There are several methods for printing text files, the best is enscript -G -Pmxd filename which gives nice headers. If you don't want the headers, leave out the -G.