If you have a round face, I think you can choose a V-neck dress to expose your collarbone, which can make your face look thinner. If you have suitable clothes, you can try them on and see the effect. If you think the effect is good, you can consider this dress as one of the factors, and then choose other clothes, because in this process, you may need not only one dress, but also many clothes to deal with different occasions.
If you have a Chinese face, you'd better not choose a square-necked dress in court style, or choose a round neck dress, so that the lines of your face look softer and the effect is better. But when choosing a style, don't choose too many decorations, which look particularly complicated and affect your overall aesthetics.
If you are a woman with a lot of facial flesh, it is best not to choose a stand-up collar when choosing a dress, because the collar above the shoulders is not covered with cloth, which will make the whole person look particularly strong. The effect of wearing a dress must be to look slim. If it is too thick, it will not look good.
A wedding should be the most important thing in a person's life. If you are still in the reference stage, you can refer to my suggestions above, hoping to help you!