I have detected dog, cat, fox, brushtailed possum and flying fox by the odours they give off. Apparently it is possible to train your sense of smell mainly by being attentive to familiar and unfamiliar odours as you go through your day. Here are a few other tips.....
http://www.wikihow.com/Improve-Your-Sense-of-Smell
http://www.wikihow.com/Improve-Your-Sense-of-Smell