3D printers are seriously cool, but as of right now, they are new technology and pretty unreliable. I have a year of 3D printing experience, and I have tried and failed again and again trying to print various models on my printer. However, after failing that many times I have learn a thing or two about settings and tricks to get 3D prints right the first time. If you have any questions, ask away in the comments, and please vote for me if this is helpful!
This is probably one of the most common ways any 3D print can fail. 3D printers work by building up objects layer by layer, and if the layers come off of the bed, you usually end up with plastic spaghetti instead of a clean printed part.
Three things contribute to bed adhesion:
The best adhesion I've found for ABS consists of a 80-90° bed, PET tape, with a thin film of Elmer's Glue stick on top.
The best adhesion I've found for PLA is a 0-50° bed, PET tape or uncovered glass, and Elmer's Glue.
Suggestions and methods from comments include:
Use hair gel from the dollar store on hot glass for rock hard adherence with PLA.
I print ABS at 220 degrees Celsius on a 110 degree bed.