The first vase I owned was a glass cylinder from a grocery store, the kind that comes free with a bunch of flowers if you buy both. It taught me that a vase is really just a container for water, and that the container matters a lot less than what's standing in it, until the flowers die and you're left staring at the container for the next three weeks.
A good vase or a decent fake plant will sit wrong in a room before it sits right, and the usual culprit is scale, not style. A tall, dramatic stem in a small apartment living room can make the ceiling feel lower, not higher, because your eye reads the top of it instead of the space above. Heavily patterned vases fight with a room that already has a patterned rug or busy curtains, you end up with three things shouting at once and nobody wins. And artificial plants with glossy, uniform leaves look fine from across a room and like a shop display up close, which is the exact wrong place for something you're going to pass every day on the way to the kitchen. If the room gets strong afternoon light, that's actually where fakes do best, because real plants either burn or sulk in a west facing window and a good faux fern just sits there looking smug about it.
If you've got nothing on a shelf right now, start with one plain, solid vase in a neutral color, ceramic or glass, nothing printed on it, and let whatever you put in it do the talking. That one piece will work empty in winter when there's nothing to cut from the yard, and full in spring, and it won't argue with anything else you bring into the room later. For scale, measure the shelf or table depth before you fall for something tall and narrow in a store, because a vase that looked reasonable under bright retail lighting can tip the whole surface visually once it's home under a lamp at eight at night. As a rough rule, a vase or plant should take up no more than a third of the surface it's sitting on, and the mistake almost everyone makes, myself included, is buying for the gap on the shelf rather than for how the piece will look from the doorway, which is the angle you actually see it from ninety percent of the time.
So before I buy, I ask myself one thing: if I walked past this at seven in the morning with the lights off, would I still want it there, or did I only like it under the store's spotlights?