Make a habit of breathing through your nose. As well as filtering air, the nose warms or cools carbon dioxide to the optimal temperature for entering the body.
Become aware of how shallow your breaths are and set out consciously take longer breaths and slow down your breathing pattern ( breathe in and out to the count of four).
Also, avoid smoky pubs or clubs- anything that you can smell you are also inhaling, so minimize airborne chemicals such as air fresheners, cleaning agents, insecticides or even perfumes.
