Not sure if this is true with the NX250. DemostiX probably could comment better. It's true with the NA/NX200/Tropical versions though.
For hanging - hang it - get in - close the zipper. If the zipper is hard to close at the finish you are strung to tight. If the netting is loose after being zipped closed, the hammock may be too loose (although you might find that more comfortable). Main thing is be sure you are not so tight you stress the netting - just go something less than that to find a comfortable hang for you.
The foot elevated thing is really important with the bed fabric Clark uses. It's awesome to have mosquito proof fabric, it's also pretty slippery. You'll know if you don't do this, and you'll not do it again. It's not a cause of imminent death, just not comfortable and you'll be loving the pull loop at the head as you'll need it.
Then - after you find the right tension - get out, close the netting and storm shield, and take a look at the hammock. See how low the storm sheild droops towards the hammock sides and try to get that droop each time you hang. If the low part of the droop is midway between the hoops, you are nearly level. If the low part of the droop is at about the 1/3 way going down from the hoop at the head end, you are hung with the foot end elevated which is the preferred angle for most.