Is there a one or two word expression for 'adding to the beauty of' as in placing something in a home?
Beautify, spiff up (colloquial), decorate, adorn, bedeck, deck out (colloquial).
There are more synonyms here.
Deck the halls
Usually a phrase for decorating the house. Used in Christmas songs/poetry, so you can use for other occasions, but it will remind people of Christmas.
You really spiffed up the place!
Something you say if visiting someone and they decorated it for the occasion. I'm not sure how common this phrase is. Spiffy is the adjective and I usually hear it for nice clothing. (I'm from New England in the US, I don't know if this would be recognized elsewhere.)