While having your dog throw up in front of you may cause you to be concerned, there is usually a reason that is common and natural for most dogs. Dogs will eat grass from time to time and this causes their stomachs to become upset, thus they will vomit. If your dog does this every once in a while, and there are only a handful of instances in a couple months, there is usually nothing to worry about. Issues should start to concern you when this is happening more than once within a twenty four hour period.
When you notice that abnormal vomiting, or more than twice within twelve hours, is occurring you should seek the help of your vet. If you have recently changed over your dog's diet to something different, such as buying a different brand of food because you did not have the money or the store was temporarily out of the brand you normally buy, then you should wait 24 hours and feed again. While your dog's system can get stressed by such changes, after 24 hours you should be able to feed him or her and nothing adverse will happen. This is just a minor stomach issue due to different food.
If your dog is showing signs of abnormal vomiting, such as more than once in a few hours or persistently over a 24 hour period, you should immediately stop feeding your dog for at least 24 hours. This will give its digestion time to work the last meal out of the body. If you notice a strong odor in the vomit it could be caused by an intestinal obstruction and your vet should know immediately. If the vomit has undigested food in it, it could mean overeating, anxiety, or food poisoning.
If your dog has not vomited within the 24 hours that you have taken them off food, you can then start them on a bland diet and see if they keep it down. While on this 24 hour fast you can give them water and ice cubes to help keep them hydrated. If they are vomiting after water or ice, take them to the vet immediately as there is a good chance that food poisoning or some other issue is involved that will require medical attention. The bland diet should consist of small portions of rice, sweet potatoes, or oatmeal and fully cooked poultry, lean pork or beef.