This.
Also look up at the tree, if it looks dead, limbs have been falling off etc pass on it. Don't forget trees get thinner as you go up, so set your base "up" a little so it will not slant downward once you get higher.
Practice in your yard before you get out there. That you can experience what you need to have, saw, cellphone and knife on your body, pull rope, extra screw in hook/holder. Get the seat set up too.
Last but most important do not use a rope/cable to hold your feet in the base. If you fall you want your feet to separate from the base. You don't want to be hanging upside with broken ankles and cant get free.