Remove the plant and add a large decorative mirror.

which side would be best for a mirror? Side where the door opens or the opposite?

Work with the side that the plant is on, so there is no possibility of anything hitting items you place there. Welcoming Design Ideas For Small Entryways

I don't think you need much -- the plant seems ok, or an umbrella stand if you come in and out this way. If you find something you like, then either wall is ok. If you need additional functionality here (not just for decor purposes), you could move the plant to the other side and put a little shelf for mail or whatever, with a small picture or mirror over it. Otherwise, I like the rug and I'd update the chandelier to something with maybe some black metal elements...

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Your rug is fine, but I would get one that covers most of the landing area. Remove the plant. Add a large, square piece of artwork to the left side of the door, and a smaller round mirror and very slim shelf in the right side.