Most wine is ready to drink when it is sold .. only some (usually the more expensive) will keep for any length of time. So don'tt keep them too long or they may go off before you get the chance to enjoy them.
Wendy's answer is especially true for white wine. You really need to drink that within 6 months. Reds will last longer, but remember to keep them on their side so that the cork remains wet(unless you have got one of the new plastic corks, in which case it doesn't matter as much).
Few wines are improved by long keeping. Tell us what you have and I'll tell you if they would improve after further keeping. Or buy Hugh Johnsons Pocket Wine Guide 2003 and he gives the vintages of thousands of wines showing their maturation. If your wine isn't listed then its probably not worth keeping, but there are general vintage charts for regions in the book also.