Learning to use one your most sensitive organs, your nose.
Why bother sniffing wine before you taste? Because your nose is hundreds of times more sensitive than your taste buds and will tell you more about the flavor of a wine (or any potential defect) than by just drinking it.
For many people this is the beginning of the intimidating part of wine tasting. What am I doing? Take a deep breath. Not of the wine, but to relax. This first part of sniffing the wine is simple.
You are checking for "off" odors. Does is smell moldy? Have a strong vinegar smell? Does it smell like nail polish remover? This sniff isn't to detect the fine subtleties of the wine. It's to make certain the wine has not gone bad or detect obvious flaws in a wine's aroma.
Wines that have "turned" can be detected by a sniff. Oxidized wines smell stale and should not be drunk. Any bad smell can be a reason to pass on a wine. But, be careful, when training your nose you need to know how to recognize "bad" odors. Some novice wine drinkers are not used to certain smells.
Sniffing wine is a simple process. Hold the glass (again only filled 1/3 with wine) an inch below your nose. Don't stick your entire nose in the glass. Take a couple gentle sniffs. Is there anything off about the smell? You may encounter unexpected odors. This is different than an "off" smell.
A good way to begin to distinguish unexpected smells is to smell three quality wines from the same type (e.g., Shiraz). This will help you distinguish common smells among a varietal. You will soon learn to distinguish the unusual from the bad.
This introductory sniff will give you a better idea of the wine's aroma after we next swirl and smell the wine.
Words of Caution
Be aware of what is around you. Is the person standing next you wearing heavy cologne? Are there strong food odors? (This is more likely to occur in a meal setting than a formal tasting.) These will effect how you interpret the wine. You can "clear" your nose by smelling a piece of bread or a glass of water (filtered please).
Next: Swirling your wine like a pro! How to Taste Wine III
Have you read the first part of this series? How to Taste Wine I