Girls, remember: inserting a butt plug takes a lot of preparation and care.
Never go for it if you are not 100% sure (110% is even better).
Do not forget the lube. The water-based are better I think. They are more universal (you cannot use silicone lubes with the silicone toys), but silicone lasts longer. Hey, you are not in a hurry, remember!
Calm down and take your time (at least for the first time).
I found it important to choose the one with the smooth transition between the inner and the outer parts. Makes it easier to take it out afterwards.
Now will have to wait and practice a bit more before actually showing this to anyone interested in my butt.