When it comes to making something good great there is an old saying that applies--it's all in the details. Pay attention to them and the most informal or smallest affairs can become much nicer than expected.
One such important detail whenever it comes to entertaining people is table linens. They are an essential base to the décor of any party or function. The table the guest book is on will have one. If you have a gift table or buffet they will need them to. If you're having sit down style eating or just cocktail style you'll still need linens for those tables not to mention the napkins.
The right kind can totally set the tone for the type of event that you have. If you are going for a more formal event a white damask weave, Jacquard weave, or plain white linen or cotton are often used. Less formal to casual affairs may use different colors or patterns.
Size will be determined by what the table linen is used for. When it comes to buffet tables you want the linens to be touching the floor. This is so that whoever is working the affair can use underneath the table to store and hide things that may be needed during the party. For the tables people will eat at you want your tablecloths to hang from 8-18 inches off the table.
When it comes to your napkins the rules are pretty simple. If it is for a formal affair you want the napkins to match the table linens. However, for more informal or casual affairs it is okay if the colors are not the same.
Table linens can last for a longtime if cared for properly. When you store them you want to make sure they are clean and dry. Do not use any starch prior to storing them for lengthy periods of time. You also want to make sure not to store them anywhere that the temperature tends to fluctuate since this can damage the linen.