Wine is meant to be enjoyed in moderation. When a full 750 ml bottle cannot be consumed in one sitting, recork it and enjoy it later. Do it right and you can keep the remaining wine fresh for three to five days.
After it's removed, a natural cork can puff up and become larger than the bottle opening. Usually a little patient twisting is all you need to get the cork back in. You don't need to push it all the way back in. Insert it just far enough to create a tight seal.
If the cork is damaged or is old and crumbly, wipe off any loose bits and examine it for cracks. A damaged cork may still adequately seal out the air, but if it is badly damaged, find another closure. Replace a damaged cork with a rubber wine stopper, or cover the bottle opening with plastic wrap secured with a rubber band.
If your wine came with a screwcap closure, you may be able to screw the cap on again. If you threw the screwcap away or it isn't sealing tightly, use a cork from another bottle, rubber stopper or plastic wrap to seal the bottle.
To keep opened wine fresh for as long as possible, store the wine -- white or red, it doesn't matter -- in the refrigerator. Chilling slows the movement of oxygen molecules in the bottles and delays the oxygenation of the wine, which is what causes a wine to develop off aromas and flavors after being opened.
You do not need to store the bottles on their sides after they've been opened. Storing wine bottles on their sides is meant to keep natural corks moist over years or decades. Once bottles have been opened, they have a shelf life of less than a week, so the cork condition isn't that critical.
Remove red wines from the refrigerator a half-hour before serving to reach the recommended serving temperature, which is 55 to 60 degrees Fahrenheit.
Some wine accessories can help to prolong the life of wine. Spray bottles of nitrogen or argon can be used to replace the oxygen in the bottle with inert gas that will not interact with and decay the wine. Studies have shown, however, that refrigeration works even better than inert gas.
If you've accidentally pushed the cork into the bottle, don't hesitate to serve the wine. After all, the wine has been in contact with the cork during its entire life, so it won't hurt anything to have the cork floating in the wine now. However, if the cork is old and falling to pieces, decant the wine before serving it to remove the cork dust and crumbly bits.
For a cork that is stuck in the heck of the bottle, use a pen, pencil, chopstick or other utensil to push the cork all the way in. Replace it later with a different closure.