Put a hole in it!
I've gotten into the habit of adding a loop or a hole in my models so that at least the object can be hung from a backpack, used as a zipper pull or put on a keychain. This is especially meaningful when teaching a beginner or a group of younger students, as it gives beginner 3D printing enthusiasts a way to show off their work and start a conversation about their new hobby ("Yo, what's that plastic bulldog hanging from your backpack?").
The first time I did this was with the first model I ever printed on my printer. I found a great simple set of Minecraft (tm) tools on Thingiverse. They were cool, but very useless. I simply added a keychain hole to the handle of each of the four tools and they definitely became more useful - or at least displayable.
There are two simple methods to achieve this.
First, you can actually punch a hole in the model by subtracting a round circle from the main model with a cylinder. This is the best method for the flat models. I've found that about 4mm is the right total diameter to make it easy to get a key ring into the hole - but it also matters how much material you leave around the hole. It seems that 2-3mm is about right to get enough strength with not too much width to get a keyring around the material.
I try to pick a corner of the model for the hole to give more clearance for the keyring. Sometimes you can get lucky and the hole can become a natural part of the model - like in the Twitter bird name tag examples in the post about name tags.
|TinkerCad Torus shapes|
If you use the second method, remember to add the ring (torus or hollow cylinder) to a place which is conducive to successful printing - not floating out on the side of the model which will require supports or just fail to print right.
Doing this in TinkerCad or 123D
In TinkerCad - you're either using the "cylinder hole" object - aligning the hole object with the place you want the hole - or using a torus, which is offered in a few different ways in the Geometric Shapes category.
In Autodesk 123D Design - you've pretty much got the same options - using a Cylinder and subtracting that from the main object to punch the hole, or using a torus and adding it to the model in a position which will let it print successfully
|Sometimes, the hole can be part of the model (birds eye)|