bring the rooks to the center if possible, especially the opposite side. if there is only one open file try to double them on that file
Back Row Rooks

I'm struggling with the same problem, is there any principle for a closed position? I try to put my rooks behind the pawns I wat to push for opening a file to give them extra support, be it in the center or the neighbouring c and f files. Does that makes sense for a guideline?

One other point I've been 'forced' to keep in mind - as Black - is that if White has that old Q behind B looking down the a2-g8 diagonal with the Kingside white Knight lurking nearby then...
Moving the f (0-0) Rook to the center, or even the open C file can be good as far as providing an escape route for your Black King. If, for example, you move your Rook on the a file to your open c file, then your King could get trapped with no escape if the 0-0 Rook on the f file is still at home. Not that you'd fall for any traps down there but....just sayin'.

and Roman has tips in his today's video - 8/15/2013 - Re: which back rank white Rook to centralize in a KIA game.
http://www.chess.com/video/player/member-analysis-wrong-rook
Assuming in the opening moves that your opponent has let you develop all your bishops, knights and queen to their "best" positions - does anyone have any advice on where to best position the Rooks on the back rank?
Yes, open files are a good choice but not always easy to figger out which Rook (left or right) goes on the open file.
Also if there are no open files then x-raying a queen might be good but what if there is no queen to x-ray and there's no open files.
I'm never quite sure where to place rooks and which rook goes where.
Does this signify the beginning of the middle game with *shudder* a plan?
Thx.