Every child loves to climb trees and we can all agree that it is good fun when undertaken correctly. So here is the golden rule of tree climbing. Pass it on
Both feet and both hands, taken together, provide you with four points of support. At any given time while climbing, at least three of these points should be securely supporting your weight. This is the "three-point rule". When this is true, and you are ready to continue up/down the tree, move only one point of support to a new location - at all times leaving the other three points secure. When the fourth point is secure, you may move one of the others. A point of support is secure when your entire weight, including everything you are packing, can rest safely on that point. Further, each point should be secure on a different support. Having two feet on the same branch provides you only with one point of support. It should go without saying that if the branch cannot bear your weight, then it cannot be said to be secure.
You may think that it is overkill to have three different points, each of which can support your weight, but branches break, feet and hands slip, and the unexpected happens. Thus, when following this rule, any two points of support can fail while another point is reaching for a new location and you will not fall.
It may be hard to judge the suitability of some branches for support. You may test one by using your free point of support, so long as the other three points remain secure. If placing your entire weight on the branch causes it to slant down from the trunk, do not use it.
Note that sitting on a branch does not provide you with a point of support, even if you are straddling it.
When using a branch for support, use the part of the branch nearest the trunk, where it is the strongest. Don't use branches which slant down from the trunk - only use those which slant up or are perpendicular to the ground. When using the trunk of the tree for support, your arm should be able to reach at least half way around the trunk - any less and you cannot use that arm to hold yourself in place.
Other points
Don't wear baggy clothing or articles which can catch in branches and unexpectedly yank you one way or another while climbing. And never wear anything around your neck (such as straps, necklaces, or ties) or you risk hanging yourself.
Wear footwear that provides good traction.
Pick your tree carefully. A tree with a lot of moss or lichen on the branches does not allow you to obtain secure support. Likewise, a tree which is diseased or rotten may break apart while you are climbing it. A tree which cannot be climbed without abandoning the three-point rule (most likely due to branch placement) should be avoided.
Do not climb a tree with a wild animal in it, although birds and insects can usually be safely ignored - unless the tree is a nesting site for them.
Avoid trees near power lines. You don't want to be electrocuted.
Wear a helmet. The kind of helmets worn for bicycling will keep your head safer if you do fall, and can prevent injuries due to branch/head collisions. Rock climbing helmets work even better.
Do not use the spikes or gaffs used by pole climbers - these can damage or even kill trees.
Happy Climbing