Well first the condition it's in, make sure the pins on the connector are all there and not bent/broken.
Connector type of course, does your Video Card output VGA or DVI, try to match this with the monitor.
Dot pitch - Common sizes of dot pitch range from .31mm down to .25mm. Its easy to remember the smaller the number the better here. Monitors that have a smaller dot pitch usually have higher resolutions as they can fit more pixels on the screen at once.
Refresh rate, while 60 and 75hz is good 80 or even 85 is better!
The refresh rate is linked directly to the resolution of your monitor. If you set high resolutions on your monitor it has more pixels to scan and therefore takes longer to complete a full pass of your screen. This in turn lowers the maximum refresh rate that you can achieve.
But your best bet is to hook it up to a computer and give it a test run (if possible).