Yes, there was an order, or precedence, as you may say.
In the order bar (ordensschnalle), for example, a Prussian would have the Iron Cross 2nd Class placed first from left to right. This was to be followed by other Prussian awards, like the House Order of Hohenzollern and others. Then, the orders from the different states followed in order of importance.
However, this could be different for a Saxon or a Bavarian. For example, a Saxon, could consider his native land orders more important than those of Prussia, so he would usually place his Saxon awards first against convention, as
Max Immelmann did.
A wonderful source of information in English is the series of books written by the late Neal W O’Connor on the aviation awards from Imperial Germany.
For a great discussion on Imperial Awards, you could go to The Gentleman’s Military Interest Club (GMIC), a forum with very knowledgeable people that can provide you with a lot of information on this topic too.