A considerable amount of strategic planning is required to ensure that maximum effect is gained from sending Christmas cards. Timing, size and quality are of paramount importance.
Sending Christmas cards too early is not only ineffective but can be humiliating for the sender. It reveals one's position, discloses the size and quality of card, exposing oneself to the possibility of a devastating counter-attack. On the other hand, a very late Christmas card runs the risk of negating the recipient's ability to respond, and reduces one's total card count.
It is certainly better to be on the early rather than late side, for the get-in-quick Christmas card sets the pace and compels the opposition to reply. It is a brave opponent who will respond with less than an equal-to or better-than card.
The next thing to understand is the value of size in Christmas cards. Important people, or at least people who think they are important, send big and important looking Christmas cards. This makes the recipient feel small; which is precisely what is intended. This can be quite costly, but usually worth it.
There is also a place for very small and/or very cheap Christmas cards. They imply bad taste, poverty or disrespect to the recipient, and will guarantee deletion from their Christmas card list. These are particularly effective for terminating pointless long term Christmas card exchanges with people like the Fanshaws you met in Torremolinos in 1976, and can't even remember what they look like anymore - or was it Benidorm?
First-time Christmas cards sent on impulse to recently made friends should be avoided, for they can have devastating consequences; like those nice Watson people you met in Benidorm. Whilst it might be a nice surprise to get a lovely card in return, you might not be very pleased when they arrive at your front door on Boxing Day - or was it Torremolinos?