Usually each badsector on a disk will remove a few lines of an MS Word document, for instance. When you buy disks, remove the individual plastic wrapper they are shipped in. Putting them in and out of that envelope can build up static electricity and damage your disk. You should keep disks in a container, however. Never leave your disk on top of a TV, speaker, or monitor, as these containmagnets that will damage your disk.
Temperature can be a problem as well.
We usually see twice as many problems with recycled disks than with regular ones. Get a new disk every few weeks. Don't depend on one disk for an entire semester. When you use an ITS computer, copy your paper onto the hard drive before you work on it. On a Windows PC, doubleclick on My Computer.