Happy/Wanting to play
Ears will be pricked forward and tail wagging
Eyes will be bright and happy and mouth open slightly but teeth covered and dog may be panting excitedly
Dog may be bouncy, circling, yipping, mock growling
Dog may play-bow (lower front end with tail high in the air and wagging)
Aggressive
Dog will try to make himself look big - hair on back and shoulders raised and he will be up on his toes
Ears will be pinned back and eyes narrowed
Body will be stiff and tail out straight or raised up slightly
Teeth may be shown with or without snarling
Dominant
Dog will be standing tall as he can with or without hair on shoulders raised
Mouth closed
Ears erect and forward and eyes wide
May be woofing or growling
Tail raised high and may be wagging like an old metronome - "clocking"
Fearful
Dog will cower down and try to look smaller
Ears will be pinned and eyes averting gaze
May show teeth
Tail will be tucked and dog may back away
Dog may be shivering
This is just a brief look at some more common dog body language. Dogs who are acting aggressive, dominamt or fearful are more likely to bite and should be left alone.