I just quit smoking a week ago and I can smell Emma much better now! I got some dog biscuits that help. The funny thing is she mostly has morning breath! She crawls up the bed to me first thing in the morning and breaths on me! I can smell the rest of her better too! And it's too cold here to bathe her.
Clean teeth makes a load of difference. Most of the doggy breath smell comes from the bacteria that builds up with tarter. If your dog has icky teeth, have your vet clean them and then start brushing with dog toothpaste 2-3 times a week (it takes 3 minutes once your dog is used to it).
Tarter build up on teeth can cause heart, liver, kidney, and lung problems as the bacteria enters the blood stream. It will shorter your dogs life. Keeping teeth clean is easy and takes very little time - but not everyone knows about good canine dental care. We learned the hard way when we lost our first Sheltie 10 years ago to heart problems that almost certainly stemmed from bad teeth.
Good food makes a difference, as does providing bones and other chewing action. :)