Some typical signs that your dog may have allergies to inhalants or fleas are:

Frequent Itching
Chewing and Biting (espcially on the tail, the stomach, or inside of hind legs)
Licking and chewing paws
Sneezing, Coughing, and Watery Eyes
Hives and rashes

Inhalant allergies usually are stronger during spring and fall. Flea allergies are more prevelent during summer.

Another possible suspect that your dog might be allergic to is your pet's food. Typical allergins that are found in your pets food are:

Corn
Beef
Dairy Products
Wheat
Soybean

Working with your Vet you can determine what type of food allergy your pet may have.

There are a few things you can do right away to help with your dog's allergies:

Vacum and dust frequently

Shampoo with Aleo Vera or Oatmeal shampoo, this will help sooth itchy skin

Switch to stainless steel bowl, some dogs are allergic to plastic

Groom frequently, pay close attention for fleas.