Testing the Lights
Few things at Christmas time are more annoying tha stringing lights around the tree and then plugging the cord into the outlet only to discover that your lights do not come as planned. It is so easy to test the lights before you begin decorating that there is absolutely no reason to ever have a string around the tree before trying them out.
How Many Lights?
A general rule of thumb states that for a properly illuminated Christmas tree you need at 100 lights for every foot tall the tree is. A 5-foot-tall tree would need 500 lights, and a 10-footer would need 1,000 lights. The problem with this rule of thumb is that a 10-foot-tall Scotch pine is going to be much fuller than a 10-foot-tall Fraser fir. Begin with the 100-light rule, but take into account the thicker qualities of spruces and pines over firs.
Stringing the Lights
There is no single perfect approach to stringing lights. Some people prefer to work from the top down, while others begin at the bottom and work their way up. Of course, if you choose to use those netting lights that are simply tossed over the tree like a net and pulled down, you avoid the whole situation. The one thing you will want to keep in mind while stringing Christmas tree lights is that removing the strings will be much easier if you make sure you decorate with one string at a time and begin from the spot where you ended. Do not allow the strings to cross over each other, or you will face the difficulty of trying to sort out strings as you are pulling them off. Since these strings are so difficult to sort out by themselves, you want to avoid compounding the problem.
There is one exception to the rule about not crossing strings. Some people prefer to decorate around the trunk of the tree from top to bottom (or bottom to top) with one or two strings and then decorate the branches secondarily. This can create an awesome effect, as long as you make sure the branch strings don't intertwine with the interior strings.