Well, I use logic.
Firstly, I ask myself what the worst thing that could realistically happen is. Generally this is enough, because my higher brain can rule out all those ridiculous ideas that creep in occasionally.
If need be, I then ask myself honestly whether feeling nervous about something will in any way help the situation... and of course, it won't. Fear is just an inbuilt psychological reaction, designed to help us flee from dangerous predators and the like.. not something that is designed to tell us how to behave or live our lives.
The amygdala, the part of the brain responsible for fear, is one of the most primitive parts of it. It controls arousal too, so its not all bad lol.
Anyway, I don't believe there is any quick fix to it all, but anyone with the desire to can, gradually overcome their fears. As others have already pointed out, this is best done by facing them head on, although there is nothing wrong with doing it slowly.
Personally, I do have a mild phobia of rats, but since this doesn't impact on my daily life I've never really done much about it.