First be sure he has a temperature by taking it rectally. If using a digital thermometer wait until it beeps to read it, otherwise leave it for a full minute before reading. A dog's temperature is 101-102.5F.
If your dog's temperature is over 103F, you can use a damp cool towel or ice packs on your dog's abdomen and feet to try and cool your dog down. You can also use alcohol on the pads of you dog's feet. Offer cool water (not cold).
If it is over 104F, don't wait, take your dog to the nearest emergency Vet.
Dogs don't get colds like humans, but they can develop upper respiratory illnesses such as kennel cough and canine influenza as well as bronchitis and inhaled allergies. You can read about bronchitis here:
It’s possible that sneezing and nasal congestion can be due to an allergic reaction to an inhaled substance. If this is the case, Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours.
You can read about these here.
Kennel cough is normally contracted when a dog has been boarded or kenneled or around a large number of dogs such as at a dog show, dog park or pet store. So if he starts coughing, it may be this. Here is a website with more information on kennel cough. http://www.thepetcenter.com/gen/kenc.html
Canine influenza is now becoming more prevalent and like it sounds it is a canine flu. Here is an excellent site on it.
You will want to monitor your dogs condition looking for colored discharge from the nose or eyes, a productive cough (coughs stuff up), stops eating or lethargy. These are signs of a possible bacterial infection as well and my require antibiotics. If your dog appears to be having a difficult time breathing, you will need to see your Vet as some dogs dog get really sick with canine influenza and need support to recover.
To help your dog breathe easier you can run a NON-medicated humidifier in the room your dog is in, or sit in a steamed up bathroom with your dog to help keep the mucous moving. Robitussin DM at a 1/4 teaspoon per 5 pounds can be used to control the symptoms. Dosages can be obtained at this website. http://www.petplace.com/drug-library/dextromethorphan-robitussin-dm/page1.aspx
If your dog has not had all its vaccinations I urge you to have your dog seen as soon as possible.
I hope this information is helpful to you.