I've never been a great one for writing letters.
我向来不喜欢写信。
She hasn't written ─ not that she said she would.
她还没写信来——倒不是她说过她要写。
This expression is used mainly in speech, not in writing.
这种表达主要用于口语，而不是书面语。
Get everything in writing in order to cover your back.
一切都要立字为据，以绝后患。
He told us not to write more than three sides.
他告诉我们写字不要超过三面纸。