Well, since I've known how to speak English most of my life (technically my second language, but also my primary language), I tend not to be actively aware of the somewhat arbitrary rules there are out there for it. That being said, I don't think there is any particular "secret" as you say, and that what is most difficult differs from person to person. That being said, English spelling can sometimes be highly arbitrary (often because of historical reasons and etymological roots). However, depending on for what you want to use English, I don't really recommend worrying too much about spelling and focus on trying to speak. Cheers.

personally, I hate words with like receipt, believe because I always have to think twice about the spelling! I also struggle with the trailing S, like John's leaving (john is going) Johns leaving (what john has left) and 'there are two johns leaving' Keep it up though!