There are a number of settings on the camera to check first. Use auto-focus and macro-settings. Use the largest pixel setting (you can re-size them later).
You should get as close to the glass as possible (right on it is good). A tripod is better to minimize the "shake" when you snap the shutter. Turn off all room lights to avoid light reflection.
Some folks abhor the use of flash due to the reflection coming back. Keep in mind that the flash allows the camera to capture your image (slowing it down so to speak). If you decide to use flash, angle the camera so that the flashback doesn't appear in the photo.
Here are some examples with using flash: