Riesling should be served chilled but not ice cold.
Most inexpensive Rieslings and New World examples are ready to drink when released. Typical French examples can age for several years and high-quality German spatlese, auslese, or dessert wines can age incredibly well, easily a decade or more.
Buying (and drinking) an older bottle will typically reward you with a mellower, softer texture, creamed honeyed notes, and intriguing petrol aromatics. A younger wine will be higher in acidity and offer bright lively citrus flavors and a simple grapey fruitiness.
Store bottles in a cool, dark place. While it is now common for wine makers to use plastic corks or screw-top closures which may be stored vertically or horizontally, those with the traditional corks should be laid on their sides to keep them moist.