>>1931696Know how to identify hazards, such as root loss, weak attachments, power lines, etc.
Keep your weight close to the trunk as much as you can
Think about distributing your weight and keeping yourself connected to the tree redundantly, i.e. if your handhold breaks you should already have your other hand/foot on something you can catch yourself with. If you're familiar with alpine climbing, the concept of self belay should be in your mind.
Know what you can trust your body weight on. I generally feel pretty safe on a 1" branch or bigger, but this changes based on species.
Consider environmental factors. It's more difficult and more dangerous when it's wet and windy out. Don't climb trees in a thunderstorm.
You can use a sort of locking step to chimney up between stems. You brace yourself using your feet/knees pushing against back, then push up with both hands and one foot behind you against the stem. Then match your feet and advance them. Should come pretty natural
If you can't step high enough to get your foot to the next branch, use your knees. This happens a lot.
Consider basic rock climbing technique, like turning your reaching side toward the inside to extend your reach.
Going down is easy as long as you can wrap your arms around and make enough friction to confidently control your descent
Different tree species have their own quirks. Pines are really sticky. Fast growing trees like cottonwood, poplar, ailanthus are weak wooded. Laurel and yew are poisonous
Normal people can be squares and won't like you climbing, so try to be stealthy. Stopping at the base of a tree and checking your phone until the coast is clear is a good move
Late summer or just when it's very hot is the worst time to climb because the limbs will be heavy with water and prone to breakage
That's about all I got rn. Trees are strong, you can trust them as far as you can trust yourself. Fear is the mind killer. Find the flow. Be observant and make good judgements.