You want to make a booklet. You know that (for USA at least) because you will be printing on 8.5x11 inch paper, your booklet pages need to be 4.25x5.5 inches. (If you use regular 8.5x11 pages, none of the sizes you use when laying out the book will be correct, because all the pages will need to be scaled down to booklet size.)

So you export your booklet to Postscript. Now you need to figure out how to actually print a booklet. You can go looking around on the Internet, but unfortunately most of the commands are for scaling pages to fit into booklet form. We do not need any scaling.

With your Postscript book as in.ps, the following command will generate a file out.ps with the pages all in their proper places, with correct rotations. The first command, psbook, simply reorders the pages for printing a booklet; the second command, pstops, places the pages on full 8.5x11 inch paper in sets of 2.

psbook in.ps | \
pstops -w8.5in -h11in '2:0L@1(1w,0)+1L@1(1w,0.5h)' >| out.ps

Note: This has worked great for me, except for times when I had diagrams in the original Postscript file; the resulting Postscript had extra pages and empty areas around where the diagrams should have been. I have not diagnosed the problem, but I was using LyX and Inkscape SVG files. Without the diagrams, the booklet generation worked well.