This is long and technical and only of interest to someone who takes a secret pride in having his trees more densely rigged than the masts of a sailing ship.
Tree straps: Ten feet of 1-inch polyester or nylon webbing. Using a water knot, form a three-inch loop in one end. Tie a loop in the other end that captures two D-rings. Holding the large loop, pass the strap around the tree, through the loop, and snug it up. Pass the hammock strap through the D-rings, belt buckle fashion, and adjust tension.
You may need to wrap the tree strap around the trunk more than once before putting it through the loop. The idea is to position the D-rings, which act as drip rings, about six inches to a foot under the end of your tarp.
I usually put my tree straps at nose level and the hammock high enough to form a comfortable chair. That is, my feet sit comfortably flat on the ground when seated in the hammock. Do add (or have ready) cotton drip strings for the D-rings.
Alternately, just tie ten feet of strapping into a single huge loop by joining the ends with a water knot. Sling this around the tree and back through itself to make a giant lark's head hitch on the tree. Put your hammock rope or carabiner through the free end loop. Less adjustable, but simpler.
Ridge line: Paracord. At both ends, loop it just around the back of each tree and tie it to itself using a tautline hitch. That way it can be slid freely up and down the trunk and tightened from either end. In fair weather I put this as high as I can reach. In rain it's easy to slide it down without getting very wet.
I use an 8-foot square tarp, pitched diagonal. So there are two tree corners and two side corners. The tree corners have 10 feet or so of paracord tied on. This goes behind the tree, just above the ridgeline back through the tie-out, under the tarp, and gets tied to the ridge line with a tautline hitch. You can slide the tarp up and down the trunk, and can center and tension the tarp without getting out from under it.
The side corners have somewhat longer ties attached, to allow the sides to be up higher for enhanced visibility. I tie the cord to the corners using a tautline hitch, and to the pegs using a lark's head or figure eight on a bight. Again, having the tautline at the tarp end rather than the peg end lets you adjust things without getting too wet.
Bear