I have a lot of experience in direct mail campaigns and have had the same problem myself in the past too! In my opinion there are a common set of principles to apply to direct mail campaigns, which also apply to a Christmas campaign – but yes Christmas campaigns are a little different!
I found thisChristmas infographic which is really valuable as a planning aid. There is a lot of information contained within the infographic but the visual format makes it much easier to digest as a reader. For me the Christmas themes section is really important as it gives lots of ideas of how to add a “Christmas layer” onto the direct mail campaign. Why not have a read through and see what you think?