Using tools such as a flash light and night lights in certain areas like stated above can be very helpful for getting over the initial fear and paranoia. In dark areas, it gives you the extra comfort of having light and makes you feel more enabled. However, in order to fully try and combat this, I would use it as a temporary defense and not permanently.
What I will do if extreme paranoia kicks in (especially when I feel monitored all the time) is take a deep breath, calm myself down and try and ignore it. A lot of time the anxiety will flare to no ends and you'll catch yourself quickly going into a sprint, lol. But try and keep yourself steady and move forward. The trick is noting that every time you are in one of those places that makes you nervous.. Nothing actually happens. Its almost like training your mind out of a bad thinking pattern. Like training a dog to some degree. Lol. Eventually, you will begin to teach your mind that it isn't necessary to fret when there is no one there.
This usually worked pretty well for me and it does take practice, but. There is nothing worse than extreme paranoia making everywhere you go miserable. So Im sorry you're having a bad time of it. I hope it gets better for you... Sometimes, the beauty of paranoia is it will just 'poof'. Hell, Ive had moments that came... then left and never bothered me again.
Anyway. Best of luck to you.