Start by looking for a bright, natural colour and pristine clarity. Clarity is a sign of health. Any wine that doesn't look fresh, but is dull or hazy, is likely sick and undrinkable. Nothing should be floating, sinking or swimming in your glass.
Colour provides clues to the age, style and flavour of the wine. Concentration, or depth of colour, indicates intensity of flavours and, in the case of red wines, of tannins, which taste bitter when the wine is young but give it the potential to age. Light reds often taste like strawberry, raspberry and red cherries; purple black wines usually have stronger currant, blackberry and plum flavours, full-bodied texture, and bitter oak and smoke notes in the finish. Pale, silvery green wines tend to be fresh, bright, crisp and lemony. Yellow gold wines with a hint of amber may have been aged in oak for rich vanilla-caramel or tropical fruit notes. Appearance is a key tool in assessing wine.
You'd think that tasting was the most important part of, well, tasting, but it's the smell of wine that's most critical. As the eyes are the windows to a person's soul, so do the aroma and bouquet tell all about the wine. Aroma and bouquet are different, no matter what the thesaurus says. Aroma is the scent that distinguishes each grape variety. It never changes, regardless of where the grapes were grown. Chardonnay from Ontario smells like Chardonnay from France. Bouquet, on the other hand, doesn't even exist until after fermentation is complete. Aging in various types of oak barrels will affect the bouquet—Chardonnay aged in American oak smells fruitier than the same wine aged in French or Hungarian casks.