fiber optic troubleshooting

I have recently taken over the job as a Systems Administrator at a local company and i have never really dealt with fiber optics before, what i need is basically a list of things that i can do to trouble shoot them. Because they are not working properly and it is 12:00 am. what i do know is that when i take the fiber from the transceivers and look at it i do see the red light so i know it is getting a signal but i dont know what to do next.