Learn English – Usage of “your goodself” and “your kindself” in place of simple “you” to refer to a high-ranking official

I would say

I was among the top 10% (of the students) when I graduated high school.

and for your other question

I got 10th rank or was ranked 10th (among the students) in my high school.

General simple guide, featuring persons 'A' and 'B'.

A: Can I have a lighter, please? B: Yes.

A: Would you like a lighter? B: Yes, please.

A: Would you like a burger? B: No, thank you.

Asking for something is accompanied by a 'please' to make the sentence more polite. It doesn't 'water down' the message - you're still asking for a lighter with the intention of getting one.

Responding positively to a question is accompanied by a 'please', while responding negatively is accompanied by a 'thank you'.

There are no formal pronouns in English. We're all impolite buggers. You'd use a 'hello' instead of a 'hi' in formal situations but English speakers never look for formal or polite constructs from their younglings.