Please guide me on how to file a successful political asylum in the USA?

Well, you're a journalist, so you should already know how to write. Basically, you need to say what you've said here, but with considerably more detail. If anything in particular happened to you before you left, you need to talk about that. go into the threats a lot more, what did you write or say that caused them. why do you take the threats seriously. why you believe you would still be in danger if you returned, that sort of thing. If you have photocopies of what you wrote in the newspapers or magazines, be sure to attach them.