Work backwards from the date it should land, not forwards from when you remembered.
Post US Christmas cards in the first week of December and international cards in the last week of November. If the cards are printed to order rather than bought off a shelf, add another week — production runs two to four business days before anything ships.
SeasonalThe temptation with a stack of cards is to write the same line thirty times. It shows. A better approach: write one specific sentence per card and keep the rest short. Thirty cards with one real detail each takes less time than thirty carefully composed paragraphs, and lands considerably better.
Older relatives, neighbours, and anyone who sends you one. The last group is the important one — a card received and not returned is noticed, and the cost of returning it is a stamp. Colleagues and friends who communicate daily by message generally do not expect one, and a card to them reads as a nice surprise rather than an obligation met.
A card that arrives on 23 December has technically succeeded and emotionally failed. It goes up for a day and comes down with the rest.
Enter their address as the shipping address and the card goes straight to them — no invoice, no packing slip and no pricing in the parcel. Worth doing for anyone you would otherwise be posting to twice.