I thought bangles were an all or nothing thing, stack them to the elbow or don't bother, and I spent ages avoiding them because the full arm stack looked a bit much against most of what I own. One on its own, worn plain, changed my mind completely.
If you've got none, start with a single solid band in a width you can actually forget about, something between a pencil and a finger's width, in a plain metal rather than anything stoned or patterned. That one piece will tell you more about whether you like wearing bangles at all than a boxed set of six ever will. The cheap versions tend to be thin, light as a crisp packet, and they ping about on your wrist making a noise that gets old by lunchtime. A better one has a bit of weight to it, sits with a slight thud rather than a rattle, and that weight is often the only real clue in the shop that you're not holding a hollow tube dressed up as solid metal.
Fit matters more than people expect from something with no clasp. Too big and it slides straight over your knuckles and off, which I learned at a bus stop watching mine roll under a bench. Too small and you can't get it on past your hand at all, which sounds obvious until you're stood in a changing area trying to force one over four fingers held together like you're diving. Measure your hand at its widest point, across the knuckles, not your wrist, and look for the internal diameter rather than guessing from how it looks on a model. Some ranges offer a couple of sizes, which is worth seeking out rather than assuming one size covers every wrist.
In the shop, or on the listing, check the opening isn't a sharp or rough edge, run a finger round the inside if you can, because cheap plating often leaves a seam that catches on jumper sleeves and eventually your skin. Check the plating itself, ask what the base metal is, because a lot of bangles are brass or alloy under a gold or silver finish that wears thin at exactly the point it rubs against a watch or another bangle. If it's meant to be worn stacked, buy that way deliberately, two or three in finishes that are close but not identical, rather than matching ones from different cheap batches that somehow never sit level.
A single good one, worn most days, tends to get more use than a drawer full of thin ones bought in a rush.