When it comes to cutting down a large tree, the most important thing you must realize is that safety is paramount. Nothing can be done without the situation being assessed. You must ask yourself what you will need to ensure that you are going to get the job done in the safest and most efficient way possible. If you feel that the job is too large for you, do not attempt on your own but hire a professional. Cutting down a large tree requires a certain level of confidence. Without it, you could endanger yourself and those around you.
If you feel confident after assessing the situation, there are various steps that you will need to take in order to cut the tree down. First, look at the tree. What direction is it leaning? Trees tend to fall in the direction that they are leaning. If the tree appears to be standing upright, what side has the most branches? The weight of these branches will cause the tree to fall in that direction. After you have figured out the direction it is most likely to fall, make sure that it has a clear path to fall. If the tree appears to be rotten or hollow, it may be better to consult a professional, as these types of trees can fall in unexpected directions. When you are about to make the first cut, make a notch on the side facing the direction you assume the tree will fall. Do not make the cut deeper than one third the diameter of the tree, for this can cause the tree to fall in the opposite direction. The cut should be made at a 60 degree angle, starting at the top and moving downward. After you have made this initial cut, you will want to make another horizontally so that you can remove a wedge of wood. After the wedge has been removed, you will want to make a horizontal cut about 2 inches about the area where the notch is flat. You will want to leave a couple of inches of wood between the notch and this back cut. This part is called the hinge. It is important that you don't make the cut too deeply and that it isn't at the same level as the other cut. This could cause the tree to kick back. Then, turn off the saw before making your retreat. Stand away from the tree at an angle but not in front or behind the area where you think the tree will fall. Be prepared. The sound of the tree falling will be startling but, if done properly, it should be the only negative thing that occurs once you have cut the tree down.
As stated before, cutting down a tree can be dangerous business if you are not familiar with using an ax and cutting at the appropriate places. This should not be something you attempt on your own for the first time.