My local parish (Saint Luke's Irving) recently posted guidelines for proper attire at the Holy Sacrifice of the Mass:
The faithful are advised not to wear caps, tank tops, Jersey shorts during Mass. Women are also asked not to wear spaghetti-strap tops, short, skimpy shors or sleeveless shirts with plunging necklines. Simply put - beach wear, lounge wear etc. are not appropriate attire.
What we wear says a great deal about what we value. If you are a public minister in the liturgy, a lector, Eucharistic minister, or a canotr, for example you should dress with extra care, so that your appearance does not pose a distraction to th worshippers. We usually dress well when we go to things that are important to us, and as Catholics, this is the most important thing that we will do each week. The manner in which the minister dresses is part of the reverence that is shown to the Lord present in the Eucharist as well as respect shown for God's holy people.