Preparation:  Gather your materials.

Step 1:  Bend your hanger into a circular shape. No need to be perfect and don't un-twirl or bend out the hanger hook portion.
Step 2:  Flatten out a plastic bag.
Step 3:  Cut the bottom seam and the handles off.
Step 4:  Cut the folds on both sides of the bag. The bag should now be two sheets of plastic.
Step 5:  Fold those sandwiched pieces of plastic together. There should now be a new fold.
Step 6:  Cut this fold. There will now be 4 single sheets of plastic stacked in front of you.
Step 7:  Fold this stack in half lengthwise.
Step 8:  With the fold facing you, cut from fold to open-end. Do this the length of the stack about 2" per strip.
Step 9:  Unfold and tie each group of 4 strips to the hanger with as equal lengths on the inside and outside of the hanger.
Step 10:  Repeat steps 2-9 until the hanger circle is full.
Step 11:  Fluff the plastic just as you would an artificial tree. Now you have a wreath!

Considerations: Grab some bows, garland, ribbon and other decorations to really jazz up your wreath.
Consider using different colored plastic bags to make it more festive and/or unique.