Hi Michael
If it is already raining I tend to give it a little while hoping that the rain will go away!
if that isnt gonna happen I make sure my bergan is out of the rain as best I can, (usually by wrapping it in a bin bag or a rucksack cover). I tie a ridgeline between the two trees i have chosen and prussick knot the two central attachment points to the ridge line and tighten, peg the four corners out using IPK pegs attached to the corner attachment loops. This works best if you pack a set of dry clothes that you only wear when you've set up camp.
If I am taking a hammock I hang it in the same way but using the corners of the poncho rather than the central attachment points so it is hanging in a diamond shape.
If the weather is fine then I hang the poncho by again putting a ridgeline between two trees but attaching one whole side to the ridgeline and pegging the other side down at a 60degree angle to encourage any rainfall to not get me, i then have an open sided shelter one end i block with bergan one end i tend to keep my feet at, once in bivi bag its quite snug and cosy and by locating the fire in front of the shelter its very warm!
i have got a 58pattern sleeping bag that has poppers which you can snap onto the poncho to make a mini sheleter but i havent experimented with this yet.
hope this helps and makes sense
cheers
Sam