Writing Christmas Cards

It is the time of the year again. I have to write Christmas cards. Most of the cards I send out are for people I don't see for many years and this is most likely the only time of the year that we communicate. However, I have to be careful what to write on each card. Some of them lost someone in their family and I shouldn't write any word like "happy" in it, and some of them are in different religion, so you should not say "Christmas".
Last year, I sent out a very Christmasy card to a Buddhist friend. I forgot about her being very much into Buddhism and sent everyone the same card saying "Merry Christmas" in front of the card. After I sent out, I realized that I sent that to her, too, but then I never heard from her after that. I was afraid that I might have offended her, but it could be that she just forgot to send me a greeting last year. After being friends for over twenty years, I don't think she was offended by a small mistake like that, but we'll see if she could reply me back this year. This year's card is "warm wishes".
When I was young, I was told to think what to write on a card and write some draft on scribbling paper before actually writing words down on the card. Check the spelling and make sure that you write right amount for the card, not too little writing to leave large white spaces, but not too much to crowd words on the card. In these days, I never take time to do this. I just start writing on a card. Since we often type, it is quite difficult to write down on paper with pens, and not having something automatically checking the spelling, I do make lots of mistakes. I even don't use whitener to clean up the mistake. I just write darker on top of the mistake. I guess this is bad.
For some reason, it is getting more and more difficult to write season's greeting cards to people. I have either nothing to write down or stupid things to write. A part of the reason that I don't write down on scribbling paper is that probably I won't be able to write anything if I do so. I also think that I write down the same thing every year. If someone had collected my cards for many years, they might find me writing the same thing for past five years or so. I want to write something personal, instead of general greeting words, but then that would make me write something quite silly.
Half of my cards are already written in that way. I have to send them soon because these are going out to overseas, which take at least a week to get to them. Maybe, I'll try writing a bit nicer and take some time to practice before writing on the actual cards for the remaining local cards.