Yes, there is a "best" (of course, what is best is in this case subjective) way of writing furigana, like this: 振{ふ}り仮{が}名{な}の書{か}き方{た}.

Other methods are sometimes used in real scenarios (e.g. Newspapers), and then I've seen the furigana written in parenthesis after the whole word, even if the word consists of two kanji split by some okurigana.

Yes, there is a "best" (of course, what is best is in this case subjective) way of writing furigana, like this: 振{ふ}り仮{が}名{な}の書{か}き方{かた}.

Other methods are sometimes used in real scenarios (e.g. Newspapers), and then I've seen the furigana written in parenthesis after the whole word, even if the word consists of two kanji split by some okurigana.