There are very few rules when it comes to networking. There are, however, lots of Best Practices that deal with effective strategies, tactics and techniques. Everything you do should be on purpose and for a purpose.
Regarding appropriate attire, err on the side of business conservative, especially if you're new to the group. It's easier to dress down from there that to dress up. You can always ask the event coordinator what people typically wear. The nature of the event itself will give you some direction. If it's the annual association picnic at the MetroParks or a networking event combined with an Indians game, dress accordingly.
Best wishes for success in Networking with more Power & Success!
Phil Stella, MindSpring Networking Editor and president, Effective Training & Communication, Inc.