As a manager, you have a certain amount of authority by virtue of your position. However, you can reinforce that by the way you dress. The Dress Code for Managers varies depending on industry, location, company culture, etc. The one constant is that a manager is expected to dress "better" than those he or she manages.
If you are new to the company, rather than having been promoted to this position from within, you should have figured out the company dress code during your interviews. You should also know the company culture. Accordingly, on your first day you will know how to dress - but don't. A first day on the job is a little like a first date. Dress just a bit nicer for the first day. On day 2 you can adjust downward slightly to appropriate clothing.