Many people are familiar with wedding attire etiquette to know that women should not wear white to a wedding. Very few people are familiar with any other rules about what should a guest not wear to a wedding. What wedding guests should not wear is guided mostly by common sense and modesty.
The cardinal rule of wedding attire is that women should not try to outshine the bride. Even if a woman is not intentionally trying to look more attractive than the bride, certain attire can make her appear prideful, insensitive, and ultimately inappropriate.
A woman should not show more cleavage than the bride. This is a common rule among wedding etiquette articles, but it is somewhat lacking. Many wedding dresses have very low neck lines. Therefore, even if a guest takes this rule literally and is wearing a dress with a higher neckline than the bride, she could still be perceived as being dressed inappropriately.
Not only does this traditional rule leave too much leeway to be suffice when considering some modern bridal designs, but wedding guests are not likely to have any clue how much cleavage the bride will be showing. An amendment to that traditional rule may be to consider having no more cleavage showing than would be appropriate in an office setting.
Wedding attire should be appropriate for the type of wedding. Sundresses and sandals that may be worn to a casual beach wedding would look disrespectful at a formal church wedding. For a garden wedding, a woman may want to avoid wearing heels as they could be problematic depending on the terrain and could also block the view of the bride.
Any material or dress style that could be considered showy is not appropriate for a wedding. Wedding attire that is perceived as trying to attract attention often appears tacky at a wedding. Lace and sequins are often considered distasteful for wedding attire.
Conservative styles can be flattering without appearing like the guest is trying to draw attention away from the bride. Ideally, the guest wants to look good and feel confident while retaining the appropriate decorum.
With the increasing popularity of nontraditional weddings, it can be difficult for guests to know what to wear. If the bride and groom having a nontraditional or theme wedding want the wedding guests to dress in a particular way, suggestions for attire are usually mentioned on the wedding inventions.