Professional wine tasters do not treat the process casually. Maybe it's not even fun at times, since they have to dissect, in minutest detail, every sip of every wine. It's their job. You, on the other hand, are not accountable to anybody but yourself. The degree of seriousness aside, there are some key factors one looks for in assessing wine. You certainly don't have to like what is considered excellent wine, but you should have an appreciation for why it is considered such. Also, it makes drinking better wines a much deeper, richer experience.
There are several kinds of tasting. One is for people who barely know the difference between red and white - uncommon but not unheard of. In this case, choose five bottles, a light young red, a mature red, a dry white, a sweet white, and a port or sherry. For a more discerning group, choose five different varietals, like a Zinfandel, Pinot Noir, Cabernet, Merlot and Syrah, to illuminate the distinct differences in so-called "red" wines. Another method might be to select Chardonnays from as many different growing regions as is practical (include several countries and states) to determine what the "baseline Chardonnay" taste is, and how that taste can vary depending upon where it's grown. This is a delightful way to explore a single varietal in depth.
For the more serious taster there are horizontal and vertical tastings. Horizontal would be, for example, ten Cabernets from the same year but different wineries; vertical means all the Cabernets are from different years. This give insight as to what constitutes an excellent Cabernet - again, in your opinion.
You can taste blind -- without seeing the labels -- or in full view of the facts. Blind tasting insures you are not swayed by a wine's reputation. You'll detect what you're supposed to detect, not what you think you're supposed to detect. In blind tasting competitions, the object is to guess correctly the wine and the vintage, and the best team wins. In competitive tastings wine against wine, such as pitting Cabernets from California against Bordeaux from France, the tasting is done blind to insure a fair out come - so the more established reputation of the Bordeaux region doesn't wield more clout than it deserves to.
When several wines are being tasted, the order should be youngest and lightest wines first followed by older more full-bodied ones. To reverse this order is to overwhelm any subtleties a younger, lighter wine might have accrued and is not a fair assessment.
And what are you looking for in evaluating wine? Appearance first, then smell, impression in the mouth, total flavor in the mouth, and aftertaste.
Appearance consists of a wine's clarity and its color. As red wines age they fade, going from deep purple to, eventually, a brick color, whereas white wines grow darker. The best way to judge color is against a white background, a tablecloth or piece of paper, with not a lot of wine in the glass. Also part of a wine's appearance is the wine's viscosity or "legs," which run down the sides of the glass when it is swirled. The more slow moving the legs, the denser the flavor. So if a red wine is pale to brickish and has slow moving legs you can expect it to be mature.
Our centers for smell are located right next to our memory centers. One good whiff of a wine that has been swirled in the glass a couple times should evoke distinct memories - of honey, flowers, mushrooms, citrus, butter, for example - it will also remind you that you've had this wine before, or alert you to the vinegary or moldy scent of a bad wine. First impressions are crucial here and far more reliable than subsequent sniffs. Based on appearance and smell, you now have enough information to determine a wine's overall quality and age.
Tasting the wine fills in some blanks, mainly with regard to a wine's "balance." Take a generous sip and swirl it in your mouth. The weight of the wine in your mouth will tell you whether it's light-, medium- or full-bodied. It also tells you how much sweetness, acidity, alcohol and tannin it contains. The object is for these elements to harmonize pleasantly. If one element is dominant, a proficient taster will know whether that imbalance is a flaw, or is acceptable in the wine being tasted. (A young red wine might be overly tannic but with definite fruitiness, suggesting that in a few years the tannin will have been moderated by the fruit; in this case too much tannin is perfectly acceptable.) The ultimate moment in tasting is just before the wine is swallowed, when the vapors hit the upper nasal cavities.
In France, the concept of aftertaste has been quantified in the form of a "caudalie." If the flavor of the wine stays in your mouth after swallowing for one second, that wine has achieved one caudalie. The more caudalies the better, especially with the wines of Burgundy. Really good wines make the strongest impressions with their smell and their aftertaste.
If you're a professional taster, or if the information obtained is to be used for any important purpose, like a wine review, you should spit out each sip. Not as much fun, for sure, but it does make for a clear head.
Finally, it's a good idea to keep notes about the wines you taste so you can enjoy - or steer clear of - those precise wines again, or so you can get wines with similar characteristics. And feel free to develop your own rating system. Professional ratings are very helpful in a broad sense but they can't compare to what you think about a wine.
At some point you may want to take an actual wine tasting class -- talk to your local wine shop for recommendations!!