Start with arching your back and try to get that ass up as high as possible. From now on in every new position you will take a picture of yourself so you can watch yourself later on and have a slideshow of how well you did.
The same goes for all the objects you are going to push in that tight hole. When it's in, take a shot.
Once the object has stretched you enough and you take it out, spread your ass and take a picture of the result.
So basicly 3 pictures for every object you will shove in your butthole.