。
Please pay all subscription fees by the end of this year.
Literal
Subscription-fee [topic-は] this-year-end before [at-に] all pay-[polite-てください].
予約購読 is literally 'reserved subscription' — i.e., a pre-paid periodical subscription. The phrase 今年末以前に is a formal-written time expression using 以前 ('before') instead of the more conversational 前に. ~てください is the standard polite request form. The whole sentence has the crisp tone of a printed notice.