Mostly this suggests a special occasion, or links with a past memorable occasion. The tuxedo also suggests formality, male success or strength, and sometimes authority or a leader figure.
Example: My boyfriend then came down the staircase wearing a tuxedo. When he got to me he got down on one knee and asked if I would spend the rest of my life with him as his wife. Of course I said yes, but then he opened the ring box. Instead of there being a diamond on the ring there was a small clock.
Useful Questions and Hints:
If I have worn a tuxedo, when was it and what the occasion and memories?
What is the main point of this dream, and how does the tuxedo play a part in it?
If I am not wearing the tuxedo, what is the character and personality of the person who is – and how do those characteristics apply to me? See Characters and People in Dreams