One thing OCD makes me do is check, double-check, and recheck. And then do it again. I've heard that checking is a fairly common symptom of OCD. I don't know whether that's true or not, but I know it's certainly a part of mine.
I periodically check doors throughout the day to make sure they're locked . . . and dead-bolted. When I'm in the backyard I like to lock the front door (and vice versa) so that an intruder would have to come around to wherever I am to get in. (Why, I don't know. It's not like I actually want to meet a criminal.) Of course I also worry that the door will somehow get locked accidentally while I'm out there and I won't be able to get in. My family always teases me (good-naturedly) about one of my greatest fears being locked doors, and the other being unlocked doors. Welcome to the world of OCD!
I do the same type of thing at night, except that it's a little more extensive then. I have to make sure that the toaster is unplugged, the dishwasher is set, the doors are locked, the curtains are drawn, any knives, tools, or other potentially dangerous instruments are put away, and no one is hiding in the closet. When I get into bed I make sure I have a phone and flashlight on the shelf next to me, and I set and reset my alarm clock at least three times to make sure it really is set correctly. I used to open the window a crack too, to prevent suffocation, but my brother and bad weather managed to convince me that the amount of air in the house is more than sufficient to keep us alive through the night.
I think you get the idea, so I'll spare you any further details about my checking routines. Suffice it to say that I think the constant checking illustrates the fact that fear is a big part of OCD. I once read a children's book called The Liberation of Gabriel King by K. L. Going. Without going too much into the plot, it's about this boy who is scared of just about everything, and how he overcomes his fear. In the book, he and his best friend make a list of things they're scared of. Hers has ten things on it, his has thirty-eight. Some of the fears are serious, like death, and some not so much, like the rope swing, or falling into the toilet. The day after reading this book, I decided to make my own list of fears. Like Gabriel's, mine was quite lengthy. Also like Gabriel's, my fears ranged from things like losing one of my family members or getting in a car accident to things like—you got it—locked doors and unlocked doors.
It doesn't really matter how long your list of fears is, or what kinds of fears it contains, or whether you think the fears are legitimate or ridiculous. What does matter is that you do what Gabriel did, and try to overcome those fears.
Oh, a word of warning. It's great to try to overcome your fears, but go at your own pace. Start small. This is the voice of experience. I've tried the baby-steps method, where I try to overcome my fear of germs by deliberately touching a contaminated object and then waiting for progressively longer periods of time (like, two seconds, four seconds, six seconds) before washing my hands. I've also tried the crash-course method (literally) where I try to overcome my fear of getting in a car accident by getting in a wreck. (Note the omission of the word 'deliberately' in that last sentence). I'm not a therapist, but trust me when I tell you that you will get much better results with the baby-steps method. Not to mention that your insurance company will be eternally grateful.