Personally, it has worked great for me to snort say half a milligram to a milligram... let the burn subside and judge where I am at. Then another milligram or so, try to relax, then continue.
With smaller amounts it gets to the point for me where I don't even feel it and I am fine with doing it multiple times. I have never snorted over 3mgs at once though, because the burn then is just INSANE. Not only does it feel like it burns, it feels like it is eating a hole into the back of my nose, into my brain. Once it had my eyes feeling like they were being eaten out too, and I couldn't move my eyes around fully without having really bad pain. Be careful with nasal administration, be VERY sparse with it as it seems to me like it can, and will do a lot of damage the more you do it.
I have tried 11mgs rectal before, and for the first 20 minutes or so it was EXTREMELY overwhelming. My body felt like it was going to explode with heat, it was just EXTREMELY intense on my body... but I just laid down in my bed, took a few deeeeeep breaths and over the next 5 minutes or so it subsided and turned into an amazing 6-7 hour long experience that was unforgettable. Besides the initial feeling like I was going to die for 20 minutes, everything felt AMAZING. I could have sworn I was going to die though, and after feeling better... It was amazing

So that, just not dieing could have had something to do with it.
Also one more thing to note with rectal administration... I feel like I may have had the insides of my rectum weakened or something. While working one day all of a sudden I couldn't move my leg cause it felt like something had snapped. It hurt right where it felt worse after rectal administration with 2c-e... and I couldn't walk for a week. Judging from tests with sublingual administration and how it eats away the skin under my tongue leaving a splotchy, bloody, raw area under my tongue, I would assume that 2c-e, in general, is not healthy for the membranes of your body... and that most likely, your stomach and intestines are best suited to dealing with these harsh chemicals.
Although, I have never had any truuueelyyy negative experiences with 2c-e. A lot of anxiety at some points but that comes and goes. As with anything, it's a learning experience.