Proper etiquette has varied over time and across different cultures, but traditionally, the most common practice is for a lady to stand on the left side of her man. This custom dates back to medieval times and has roots in chivalry and practicality.
The reason behind this positioning was to ensure that a man's right arm, which was typically his sword arm, remained free and unencumbered. This way, he could easily defend himself and his lady from potential threats or challenges. By standing on his left side, the lady would be less likely to interfere with his sword arm and would be positioned away from the potential danger.
However, it's important to note that modern etiquette is more relaxed, and such customs are not strictly followed today. People are free to choose their standing positions based on personal preference and comfort rather than adhering to traditional guidelines. The most important aspect of etiquette in contemporary times is mutual respect and consideration for each other's preferences and comfort.