Will mixing baking powder (arm & hammer) with warm water make a good cleaner for smoke stains on wall paper?

One very good cleaner is white vinegar. Vinegar is an acid, and although you might think of it as a food such as when used in salad dressing, it is really an acid that makes a very good all-purpose cleaner. try a little bit of this on a paper towel and see if the discoloration from the smoke residue comes off on the paper towel.