The best way to get rid of acne on your back is to wash regularly. Don't be alarmed if you do wash regularly and still have acne, this is caused by clogged pores and may need to add a acne cream to help get rid of the acne. Also try using a scrub and keeping you clothes clean, if this don't work then you might need to consult with a dermatologist. You can find more information here: http://www.ehow.com/how_5199440_rid-acne-back.html