People buy the smallest ottoman they can find because it looks cute in the corner, then wonder why it disappears the second they put a tray and a cup of tea on it. Scale is the whole game here, and most of us get it wrong in the same direction.
Fabric ottomans work almost anywhere you'd put a chair, which is the point of them. A boucle one at the end of a bed, a linen one doing double duty as a coffee table in a studio apartment, a velvet one pulled up to a reading chair for the three months of the year your feet are cold. They're forgiving in a way wood and leather pieces aren't, because fabric has give, it takes a nap, it takes a kid standing on it in socks, it doesn't show the same scuffs a hard surface would. Cotton and linen blends breathe better and feel right in summer, velvet and boucle read warmer and earn their keep in winter, so if you've got room for two, that's not a bad reason. The sizing mistake is treating it like a footstool when you actually want it to work as extra seating or a coffee table substitute. Measure the gap in front of your sofa, you want at least fourteen to eighteen inches of walking room around it, and measure the sofa seat height too, because an ottoman that sits noticeably lower than your cushions looks like an afterthought instead of a set. Too small and it floats in the middle of the room looking lost. Too low and nobody can balance a mug on it without lying flat.
Where it goes wrong is pattern on pattern in a room that's already busy, a bold floral ottoman in front of a sofa with its own loud print is a lot, and so is putting a fabric ottoman somewhere genuinely wet or high traffic, like right by the front door where boots and umbrellas live. It's also not the move in a room with a toddler and a full glass of anything, because unlike leather or a vinyl pouf, fabric holds a stain instead of wiping clean, so keep it out of the direct line of fire near the dining table.
If you've got none, start with one large, simple, solid colored ottoman near neutral, something you could put in front of a sofa and also drag over as a spare seat without it fighting with whatever else is going on in the room. A stain resistant woven fabric buys you a little peace of mind.
For a first one, I'd go with a soft oatmeal or stone color. Forgiving, warm, and it won't paint you into a corner later.