Bookshelf, fill it with books. Get some art (either your own or thrift it- goodwill can sell some cool pieces for dirt cheap. I got two framed photos with glass coverings of fighter jets, a framed photo of new york, and a framed drawing of a man for about 20 bucks.). Also, you can find wall tapestries/flags which always spice things up (check depop or amazon- i know its normie but bear with me). A desk is always good, a small lamp, and a bedside table.
as the previous anon said, old photos make great decor. I have photos of my dad and grandparents when they were young taped up. Antique malls can also provide some interesting wall art. I found a painting of angels, an old orange juice ad, and the cover of a russian magazine for $5 each at the bottom of piles, and they look classy on my wall when put up right. If you look, you will find.
if you have a passion/interest, focus on it. For example, if youre into WWII Germany, get a nazi flag, maybe a reproduction rifle, and perhaps posters of your favorite generals.
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