Tasting the wine
Important as the senses of sight and smell are when it comes to our enjoyment of a wine, the ultimate test is its taste. Take a mouthful of the liquid and swish it around in your mouth quite vigorously. Breathe as you do so, as this helps to aerate the wine and increases its flavour. After holding the wine in your mouth for 15 to 20 seconds, spit it out - or swallow it if you're not intending to taste more than a couple of wines.
Your tongue has a range of taste receptors in different places - you will taste sweetness most at the front, acidity along the sides and bitterness at the back. High acidity will make your mouth water, while tannin (which tends to be most pronounced in young red wines intended for long cellarage) will have the opposite effect.
When you evaluate the wine, first take into account its complexity and weight. Again, these qualities will depend on many factors, including the grape varieties used and the age of the wine: a fine aged Bordeaux will be far denser than a young Beaujolais.
Certain characteristics are associated with the various types of grape and even with the area where a wine is grown - an Australian Riesling might be described as having tropical fruit flavours, while a Riesling from Alsace would be lighter and have a more mineral/citrus quality.
In Old World wines, certain grape varieties tend to be associated with particular areas. One could say with a reasonable degree of certainty that a wine made from Pinot Noir grapes probably comes from Burgundy. This is now increasingly the case in the New World as well. Marlborough in New Zealand, for example, is now concentrating white wine production on its famed Sauvignon Blancs.
There is no right or wrong conclusion to be drawn about any individual wine. Describe it according to your own perception - after all, tasting is meant to encourage you to create your own frame of reference for the wines you drink. Learn about the tastes that you enjoy - and those you don't - then follow the instincts that you have developed when it comes to buying wine in a restaurant or for drinking at home.