If you must sniff them straight from the bottle, try to put a small amount of Vaseline or other lube on the areas that will touch the bottle.
Pouring a small amount of poppers on a tissue or fabric is a good choice because their effect is enhanced that way.
Another way, although it might be a bit geeky, is to make a kind of thick straw out of paper which is about the diameter of the bottle spout. You can use this to sniff the poppers, but there's always a danger of snorting them (which is obviously bad). If you can pierce the straw sufficiently, it acts like a carburetor reducing suction on the poppers. You can make one of these by wrapping paper around a thick pen, taping it up, and piercing it with a BBQ skewer.
Personally I think the straw method is good for personal use, but the tissue method is better for use while fucking. Treatment for poppers burn is just keeping it moisturized with something like Sudocrem or Vaseline. There's little you can do about it.
