Every holiday has a set of reminders of things that are supposed to be considered during that season. I think that we need these traditions and ceremonies to help us move beyond the mundane activities (such as going to work, cooking dinner, folding laundry, etc.) that must go on despite the celebrations. The visual elements are among the simplest of these traditions both to implement and enjoy.
Starting with this:

I love the way that fresh greenery makes the house smell festive.
Creating welcome:

My family has given ornaments to each child every year. For a number of years these were themed around the instruments that each of us played. I therefore have a whole collection of violin-playing angels. As Jonathan's family also give an ornament each year, we did not have the problem of a bare tree that many newlyweds have. Sometimes I have to find other ways to display the extra ornaments.

In lieu of a mantel, I decorate the top of the piano. One of these years I will find a nativity scene to sit in the center and remind us more explicitly of whom we are celebrating.

Something new this year--twiggy garland over the doorway:

The angel doll in the red apron was made for me to carry in my aunt's wedding when I was eighteen months old. The cream silk is the same as that used for her dress. Afterwards, my mom refurbished her into a Christmas angel and she has been brought out with the other angels every year. I was allowed to take her when I left to form my own home.
Every available surface can be used:

Beautiful tree!

Everything stays up through the twelve days of Christmas (until January 6th or Epiphany) and then must come down all at once. This stretches out the fun without having the tree dry out too much or having too many fir needles dropping off everywhere.