Sight

Visual assessment is the first step. A wine's color can help with identifying grape varietal, wine style, age, and faults. Tilt your glass at a 45° angle over a white background; this is why white tasting benches are ideal, but a tablecloth or sheet of paper will do. Look through the wine, noting the 'core' (the color at the center of the glass) and the 'rim' (the color around the edge); the core is useful in identifying grape varietal and wine style, while the rim can be used as an indication of age. Also look for the presence of bubbles, which may indicate faults (unless, of course, you're tasting sparkling wine). 'Legs' is a term used to refer to the process of wine adhering to the glass when swirled, hinting at a wine's alcohol content and viscosity.

The haziness of a wine will hint at potential faults, including protein instability, bacterial infection, insufficient filtering, and/or leftover yeast. Protein instability will often result in crystal formation, sometimes referred to as 'wine diamonds', in the bottom of the glass or bottle. While not harmful, these are not desirable. Bubbles around the rim indicates the presence of gas, typically carbon dioxide. For sparkling wines, you obviously want some bubbles (will discuss in depth in a following post), but small levels are common in younger white wines because dissolved carbon dioxide levels are left higher at bottling to help retain the wine's freshness. Bubbles may also indicate partial fermentation (primary or malolactic) in bottle for both red and white wines, or the presence of spoilage bacteria. 

Smell

A wine's aroma and bouquet are very important during evaluation. Before you start swirling, sniff the wine and record what you detect. Then swirl the glass vigorously for a few seconds. This will oxygenate the wine and release volatile aroma compounds. Sniff the wine again and focus on the different elements. The term 'aroma' is used to refer to flavors originating from the grape, while 'bouquet' refers to flavors originating from winemaking (fermentation, maturation, bottle-aging). Experienced tasters will be able to determine most wine faults during this stage (thus the prevalence of DNPIM, 'do not put in mouth', during sensory evaluation).

Taste

As you taste something, the air inside your mouth flows into your nasal passages. The combination of the smell of this air with the sensations of sweet, salt, sour, and bitter in your mouth is how you determine flavor. So, smell is really the biggest tool in sensory evaluation.

The proper way to taste sounds a lot more confusing than it really is, but I guess it takes a bit of practice. Sip a small amount of wine, then draw air through slightly opened lips while resting the wine on your tongue. Record what you sense: acidity, sweetness, bitterness, astringency, body, balance, flavor profile, saltiness, and anything else.

Just like with aroma/bouquet evaluation, you want to try to separate the different elements you perceive and define them as best you can. Don't get frustrated or embarrassed if you do not perceive the same as others you may be tasting with (or with tasting notes provided by wineries or critics). Everyone has different levels of perception for different flavors. Like I said before, everyone's sensory abilities will improve with practice so drink up!