Recommended: Send something (could be a letter or email) that emphasizes the vision (what they're giving toward) and tells how to give (address for checks, URL for online giving or EFT/LifeLink). Other follow-up / reminder methods include text, phone call, Christmas card, DM, voice memo, etc. Deadline for giving is December 31st. Back your follow-up deadlines before this date. Here's an example of a letter:
https://email.denisonministries.org/a-time-of-ax-sharpening