If you go to somewhere that sells Christmas trees, you can usually get the offcuts from the bottom branches for free.
I pile them up in my (unusable) fireplace with logs and pinecones and fairy lights.
I collect ivy to make a wreath.
I use more of the tree branches to line a small basket which I fill with conkers and pine cones and dried orange slices and some club hedgehogs the DC made when they were little, and I sprinkle it all with The White Company Winter fragrance oil.
I made a snowman and reindeer out of a pile of books and some paper. I can't get a decent link, but if you Google "snowman book decoration" you will see lots of examples.
I like to find quite a big branch, take it inside to dry out (start looking now) and hang it up, with lights and a few decorations, above the dining table.
If you like your decorations to be fun rather than elegant and you have a white fridge, you can blue-tack coloured paper onto the fridge to make it look like a snowman.
Basically forage for natural decorations, put fairy lights and candles everywhere, make the house smell Christmassy and then the odd bit of cheap tat from a bargain shop (I'm looking at you, poundshop robin and flowers on my wreath) looks tasteful.