Three things never to do in front of your client

1. Never openly discuss money, or money issues. If there is a valid question, bring it up in private with your client contact -- never in front of other people. Money conversations are best handled one-on-one.
2. Never dress like you're cleaning your closets, or like you're about to appear in a video as Hoochie Mama #3 or Thug #2. Dress appropriately for the site and situation. If you could rival Britney Spears, Kevin Federline, or even Paula Abdul, you're probably not dressed for business. Whether it's a short meeting or all-day presentation, remember, this is business. Dress for such.
3. Never bad-mouth. This means anyone, ever, especially to a client. If you are having an issue that needs addressing, deal with it privately, and in a professional manner. Watch how you phrase what you say -- and remember, if you come off too negative, it will reflect poorly on you, not the other person.