If your dog is coughing a lot then your dog might have either kennel cough
www.marvistavet.com/html/body_kennel_cough.html
or canine influenza
www.marvistavet.com/html/body_canine_influenza.html
Both of these are very easily picked up from another dog.
You can see if some Robitussin DM will help the dog breathe better and control any cough or sneezing or runny nose. Read here about cautions and dose info
http://www.petplace.com/drug-library/dextromethorphan-robitussin-dm/page1.aspx
You can see and hear a dog with kennel cough here
http://www.youtube.com/watch?v=amGKQX9zdug&feature=related
http://www.youtube.com/watch?v=uN3RpoU0qXw
If you see a colored discharge from nose or eyes, if your dog coughs stuff up, seems lethargic, has any real trouble with breathing, or goes off eating, see your vet as your pet may have a secondary bacterial infection that will need antibiotics or other meds.
If this is an elderly dog then coughing can be a sign of a heart issue as those can build up fluids on the chest leading to coughing.
If your dog is not a young puppy and has not been on heartworm prevention a heartworm infection can cause this sort of coughing.
Some breeds of dogs have problems with their trachea which you can read about here
http://www.marvistavet.com/html/body_tracheal_collapse.html
and that also can cause coughing.
If this is an unvaccinated puppy the symptomes you see may be from distemper virus too. You can read about that here
http://www.marvistavet.com/html/body_canine_distemper.html
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics