There are three aspects to tasting a good glass of wine and savoring its every subtle flavor:
Color
Oak Wine Racks
Tilt the glass against a white background - maybe a napkin held against the glass. Take note of the clarity of the wine. If it's hazy, you're usually not onto a good thing.
White wines range from a watery yellow to amber in color. A pale yellow will indicate a young wine, probably dry. The sweeter the wine, the darker the shade. However, age also adds a depth to the shade, so don't be deceived.
Color is a dead give-away to the age of red wine as well. When a wine ages, it loses its ruby red colour and develops a brick red, almost orange, tinge. Indeed, the darker the shade, the more full-bodied the wine.
Take care to avoid viewing the wine in fluorescent light; daylight is best. Wines tend to look darker in artificial light.
Bouquet
The bouquet is also called the nose of the wine. When you nose a wine, you use your sense of smell - so vital to tasting.
Hold the glass by its base or stem and swirl the wine around to let it give off its aromas. Then take a short concentrated sniff. With practice, you will be able to tell the difference between the clean fruity flavor of a fresh wine and the smell of cork, vinegar, sulfur dioxide or other chemicals that have affected the wine. (Since wine is composed of over 200 different chemical components that are similar to those found in fruits, vegetables and herbs, it's probably not surprising that the metaphorical language used in regard to wines involves allusions to fruits and spices etc.)
Flavor
After that, all you have to do is taste the wine! You can perceive a combination of four tastes: Sweetness at the tip of your tongue, acidity at the sides, saltiness at the centre and bitterness at the back. A balanced taste is that which has a good blend of all the ingredients -- alcohol, sugar, tannin etc. Some wines, for example, will have a greater amount of tannin, a natural preservative found in the skin of red grapes. It's a little bitter, but it helps the wine mature. Others have a pronounced acidity, while still others that have been fermented or matured in oak barrels have a distinct taste about them -- something like a spicy cinnamon flavor. In some vineyards over the world, a friendly fungus called Botrytis, which intensifies the sugar in the wine, is responsible for its unique, delightful taste.
And once you've learned to nose a wine and study it by its color and taste, you're ready to experiment!