Acoustic Room Treatment – any simple solutions?

Now that I almost complete building my hi-fi system, I’m looking for some simple setup for acoustic room treatment.

FYI, my system is currently placed on the long wall of living room. In a few months, I’ll have to move it down to the basement where there’re walls with no curtains or much decorations.

Can you suggest some simple and inexpensive setup (i.e. sound absorbing foam, bass traps, movable foam stands, etc) for my situation? Also, where do I place these foams? Behind the speakers, in the corners, and on the side walls?

In addition, I cannot put on anything permanent (such as foams fixed to the wall). I prefer something movable and non-fixture in nature.

Thanks.