A great place to start narrowing options is with the electrical requirements. How many signals do you have in total? What voltages, frequencies and currents are they carrying? This is a multi-dimensional list. Your signals could be digital, analog, power, or even a combination of all three. Also note that digital and analog signals may be either low frequency or high frequency.
2) Will the connector be operating in an extreme environment?
Many connector systems are subject to extreme mechanical conditions such as shock or vibration. A connector designed for such conditions often incorporates special features such as a threaded coupling that cannot vibrate loose or a strain relief (like a backshell) to support the wiring harness. You will typically find ratings for shock
Another common environmental concern is extreme temperature.
3) Is sealing needed to protect against water?
Certain environments demand protection against intrusion from liquids or dust of varying degrees. Environmental sealing options start with a simple protective boot and boot adapter, useful against occasional splashes. The next level of protection involves sealing the connectors themselves. If your application requires environmental sealing, the IP code system rates connectors by the degree of protection provided against dust and water intrusion.