All of them are just that: rituals. They are not rules. A few could even be perceived as pretty silly.
Let's take a look at these rituals, and whether you'd be well advised to follow them...
Examining the wine list: There is no "template" that every restaurant uses when putting together its list. Marketing 101 would suggest placing the highest-priced bottles at the top of each category, since many people will not bother to read the entire list. That sells more premium-priced bottles.
Advice: Unless you really know your stuff--how one wine compares to another, and whether the price points make sense in that context--you're better off simply figuring out what kind of wine you'd like to have, and then picking a price that's comfortable.
Examining the bottle label: Once you've ordered your bottle, the server will fetch it from the cellar and bring it back to your table. At that point, you'll be shown the bottle's label.
Advice: Absolutely take a look. Restaurants are notorious for showing one vintage of a wine on their list, but having another vintage in stock. There's usually nothing nefarious involved; wine lists, particularly long ones, can be a challenge to keep up to date. Examining the label simply assures that you're getting the bottle you ordered.
Sniffing the cork: Once the bottle is opened, the server will present the cork to you. This ritual involves the diner sniffing the cork in order to determine whether the wine is okay.
Advice: Total waste of time. A cork smells like...cork. You should feel free to examine it for breakage or cracking, which could be an indication that air got into the bottle and hastened the wine's aging process. But smelling the cork will tell you nothing useful.
Tasting the wine: Once you've examined the cork, the server will pour a splash into one person's glass. This ritual calls for the person to swirl the wine, sniff it and then taste it--again, to assess the quality of the bottle.
Advice: Do swirl and do sniff. But there's no need to taste. If the wine smells okay, it will taste okay. If the wine doesn't smell okay, then go ahead and taste the wine. A wine that smells good will taste good. A wine that doesn't smell good may taste "off," but probably will be just fine.