Most of that bad taste/smell comes from your
tongue. It is recommended to use 2 different brushes for teeth and
tongue, but hey you can use the same toothbrush (rinsing it in warm water prior to cleaning either is advised).
What else...sugary snacks, soda drink, smoking...bunch of other stuff.
Some would say going for professional cleaning every 6 months. Sure, but again 6 months visits were set by insurance companies.