This saves paper and halves the bulk of printed documents to carry around. It is fairly easy:
If the number of pages in total is odd, remember to put a blank sheet on the end after printing the even number pages to give something for the final odd page to print on the back of.
The only tricky bit is getting the paper in the right way round when putting it back in. Getting it the wrong side up will cause overprinting and getting it the wrong end up will cause half the pages to be upside down. The correct way up will depend on the particular printer.
Anyway, it only needs testing once for a printer, there are only 4 possibilities to test and the sheets of paper consumed in testing will immediately be compensated for by the first pages of two-sided printing.
Unfortunately, at least in Microsoft Windows 2k, printing just odd or just even page is not part of the operating system or basic printer driver but specific to each application, e.g. Microsoft Word 2k & Open Office 2 have it but Notepad 5 & Internet 6 do not.
Here are some workarounds that might be worth trying:
There might be some risk of jamming (but this is only from not neatly restacking the paper before putting it back in), sticking (let laser printer ink cool before feeding the paper back in) or of water soluble ink jet inks soaking through the paper and dissolving the ink on the other side (but if your printer is doing that then there is a problem to be cured anyway before you waste too much expensive ink!).
It is hassle to keep putting paper back in for short documents (especially because it gets confusing if you are queuing lots of documents in the print queue or what to quickly close or edit a document after sending to the printer) but for big documents, I find it more hassle to have to carry around (or find filing space for) twice as much paper as necessary afterwards.
I have received a suggestion of an "improved" order that does
not need one to remember the additional blank sheet when the number of
pages is odd: print the odd numbered pages in reverse order, put the
paper back in the fresh paper tray & print the even numbered
pages in normal order. However this creates a different inconvenience:
the sheets need to be individually turned over as they come in page
order 2, 1; 4, 3; 6, 5 etc..
Some single sided printers are advertised as doing double sided printing by 'manual duplex'. It is essentially the same as the method described above in this article but separating out of the odd & even pages is built into the printer or printer driver for convenience. If your printer has it then it is probably easier to use it because it won't need you to find a program capable of odd/even division of printing, should automatically add a blank terminal even page if needed and the way to arrange the paper to feed back in should be specified in the instructions or on the printer itself.