One thing I did that improved things was take a soft box, like the kind you get for storage at the dollar store for those cube things, and lined the inside with foam. We had some foam lying around, but some folks will use mattress foam or whatever.

You make the sides and back as air tight as possible. The bottom you make so that it's padded but you can place your mic inside. My mic is on a homemade stand I made with a wire clothes hanger.

The difference in sound is amazing because this cheap little set up helps to eliminate the open air sound.