I was like eight years old when I started using slingshots. I used to shoot to glass bottles, cans and pretty much anything that I could use as a target. Two or three months a year, I would take out my slingshot and use it to shoot with my friends.
I stopped using slingshots for a long time, mainly because I was told that they were "toys" for little kids. Two years ago, I bought me a Daisy slingshot and my desire to have fun with slingshots came back. I started shooting plastic bottles, but I found out that they were very dangerous as one day, I shot at one and the stone bounced back and hit me on the forehead. I had impact glasses on, so I was never worry about my eyes, but still the hit made me aware that plastic bottles are not a good choice as targets.
I started reading about how some of the members of this forum and their shooting practice at home. I read about some members that could use a towel, a t shirt or a piece of carpet to stop the shots behind the target. Most of them used aluminun cans as a regular target for shooting. I started doing the same for practicing at home.
I notice that aluminun cans are way too easy to be distroyed after you shoot at them with a slingshot. I have not a reliable source of aluminum cans and the plastic bottles were just out of the question. I wanted to use something else for target practicing, but I did not know what to use.
Finally one day, as I was practicing with my air rifle with metal bottle caps, I noticed that they where small and very challenging to hit. I took some that I have already shot with my air rifle and had a hole in them and used a piece of tread to hung them. I started to shoot at them with my slingshot from 10 mts. I noticed that it was very hard to hit them and if you hit them they would change shape, so the target would not be the same after a good hit, since this deformed its shape. It also would swing after being hit, so it became a moving target. Sometimes the wind would turn it to its slim side, so would be harder to hit. And if you hit it hard enough you could even cut the tread. I also have notice that sparks come out if I hit the bottle cap when I practice shooting close to sunset.
I use an old sweater as a background and as well as to stop the shoots in the back. It also helps me by showing me by indentantion were my shoots usually land when I miss the target. This way I can correct my shot and improve my aiming.
I have notice that my aiming had improve as well as my technique for shooting. Of course the more you pracitce the better you get.
I hope this personal experience could help you to improve your shooting. Saludos.