Proper Cable Placement.

I use reusable cable ties from RadioSnack and tie them to the rack so they don't touch powercords and possibly away from each other if applicable.

The best material/product to use is ceramic cable towers in the case of keeping audio cables off the floor/carpet. Those made by Rightway Audio are the best IMO. Getting and keeping cables off the floor/carpet creates a tremendous improvement in music dynamics, detail and dynamic range. What you are essentially doing is reducing the capacitance to ground and increasing the resistance to ground by elevating the cables off the floor. As a result, you are getting less signal "drainage" to the carpet; thus more signal gets to the loudspeaker or amp on time and intact. There is more to this simple discussion than what I attempted to summarize above.

What about power cords, should they be elevated off the floor/carpet as well or doesn't matter?

Keeping power cords (and power filters) free from any kind of vibration, as may be induced by the floor, will make a huge difference. Try it out.

I bought some of the wire clamps from Pure Note to keep my cables apart. They sell 5/16" and 3/8" diameters. See their speaker cables to get an idea what they look like:
http://www.purenote.com/speakercables.htm