Hammocks are usually seen as a way to rig a suspended bed, to avoid having to lay down on the uncomfortable ground, to sleep. However, a hammock-suspension that supports the whole weight of a person is way more than strong enough to also support a tent or tarp shelter, which are insignificant loads in comparison.
The first priority with hammock-promotion might be to avoid damaging the trees. Pick support-trees that are plenty big enough. Leave branches and boughs that are in the way, rather than clearing them. The idea isn’t just to sling a hammock, but to create a “leave no trace” campsite. The hammock-rig enables camping over ground-surfaces that are too sloped or uneven for a tent, or to sleep on.
At low elevations there are lots of sturdy, tall trees. In the high-country, trees may be scarce, short, small and weak-rooted; suitable guy-trees might then receive excessive use. In such situations, only rock should be used for guying. In sparsely-treed terrain, concentrating on a few sites with good guy-trees will again concentrate usage and lead to cummulative impact-effects.
Use a separate (wide) nylon-web strap or runner, to attach the main guy lines to trees. Don’t just pass a small-diameter high-strength line around a tree, and then load it with hundreds of pounds. Make sure the force is spread over a suitable surface-area of the trunk. Pad-material under a strap offers added protection & benefits.
Anchor-straps need to be wrapped several times around an anchor-trunk. A single wrap creates a tourniquet or choke-collar, amplifies pressures on the bark, and is liable to cut or wear into tree-bark. Using 3 or 4 wraps halts this cinching-effect, distributes pressure & force evenly around the circumference, and is also a more-stable and secure guyline anchor.
Secondary guylines are an important enhancement. The main anchor-points need to be placed high enough to get the camp up off the ground, but secondary anchors can and should be fixed at or near ground-level. Secondaries relieve some of the pressure applied by the main anchor-straps, and can eliminate side-pull. Secondary anchors don’t apply much side-force, but do pull up. Smaller trees can be used for secondaries, but beware of uprooting.
Both the main anchors and especially secondary guy-anchors are potentially subject to axial slippage. The anchor-strap can slide down or especially up an anchor tree-trunk. The lowest base of a tree also has more taper or flare, which facilitates up-slippage. Boulders or rock outcrops used for low-point anchors can be particularly prone to sudden up-slippage. An anchor-strap can suddenly ‘pop-off’ the rock. Pad-materials offer increased & improved grip for the strap, reducing slippage.
The first line of defense against the axial-slippage hazard, is to manually tug straight up on a newly-rigged low-point (secondary) anchor-strap. If it won’t come off or slide up when pulled straight up, then it will be even more secure when pulled at a lower side-angle.
Longer guys allow increased flexibility of rigging-configurations, and promote better anchor-physics (because the angles are lower). Newer synthetic fibers permit very high loads on small-diameter (light-weight) lines, making extra-long guylines a practical backpacking option. Just don’t use these tiny lines for tying to trees, since they will readily cut-in.
High-strength tent-pegs should not be overlooked, for use as low-point and secondary guy anchors (ground-stakes). Tent-pegs don’t normally require high strength, and are subject to price & weight market-factors that tend to reduce their suitability, for high-load hammock-guying. Look for ‘serious’ pegs, made of advanced materials and costing more.
Side, lateral or deflection guying allows a main hammock-sling to be displaced or pulled sideways. The main camp-suspension does not have to be in a straight line between the main guy-anchors. Longer main guylines allow for more side-deflection (they also require stronger anchors, and line). Deflection allows a camp to placed over more-favorable ground, and in rock-country avoids being pulled in against the pitch.
Don’t side-deflect from an overly-high anchor-line (or one over open air or a cliff), to lower ground suitable for the camp. If the side-guying fails in such a situation, the camp will then swing back to the elevated position (or out over the cliff), and likely dump the hammock-occupant from a height.