Always have a tree (real if staying put, fake if we are travelling) in the sort of bay window in the living room. Cards all over the drinks cabinet.
Bunch of mistletoe hangs in the doorway between the living room and kitchen/diner.
Some garlands on the ceiling in the hall - use thumbtacks for those. A wreath on the front door.
DD's advent calendar hung from the breakfast bar in the kitchen, and snowflake window clings on the patio doors. Festive hand and tea towels in the kitchen in Christmas week.
Crib on the table in front hall, another small one on the mantelpiece. Lots of candles lit and the stove going most days.
We have a Santa head "twirler" (v cheap from Eurosaver shop, like Poundland) hung over the stairs up to the attic room DD sleeps in. She has a couple of snowglobes in her room.
I'd love to have the time and energy to do garlands etc all over the place - but that's not possible in our lifestyle. A friend "wraps" a few of her living room pictures, with paper that she then rips to let the picture still be seen, but with ribbon around the frame too.
I do have fresh flowers in a vase, and usually make an advent wreath as well. I never remember to get poinsettia.