The most important thing is that keep a note of your ideal lens width, bridge width and temple length.
Secondly, you can choose sunglasses according to your usual life scenario, for example, if you usually play sports, driving or other activities that expose you to strong sunlight for a long time, then you can go for polarized sunglasses, which can help you relieve eye fatigue. In addition to this, there is no need to buy polarized function, you can just buy ordinary sunglasses and save money effectively.
Moreover, in terms of color, there is a common misconception that the darker the color, the more effective the blocking of sunlight. In fact, otherwise, be sure to check whether it is UV400, with UV400 rating, to protect your eyes from the sun's UVA and UVB frequencies. And the shade of the lens is mainly for visual comfort.