Here are some tips for evaluating wine:
First check the wine's clarity and its color. Is the wine clear or cloudy? Does it look dull or inviting? Important part of the appearance of the wine is the viscosity or the “legs” of the wine, which run down the sides of the glass when it is swirled.
Swirl the glass and take a good sniff. You will notice a wide array of aromas. Red wines are associated with tobacco, leather, smoke, dark fruit, chocolate, bell peppers. White wines are associated with flowers, apples, grass, citrus or similar crisp aromas. You made need to swirl and sniff several times to get sufficient aromatic data.
Now is time to taste the wine. Take a deep sip of the wine and swirl it in your mouth. This will tell you whether the wine light, medium or full-bodied. Also how much alcohol, acidity, sweetness, saltiness and tannin it contains. Pay attention to the way the wine changes as you hold it in the mouth.
Also called the "finish," this is the taste that remains in the mouth after the wine is swallowed. A really great quality wine will have a long, complex aftertaste.