If you're looking to book a banquet hall, you'd better do it as early as possible. Your lead time should be at least three months before your event, and 6-9 months is preferable if you're planning to use it for a wedding reception or similar event.
The type of banquet hall you book will depend on your event. If it's an awards banquet or something similar, you'll probably need just enough room to seat everyone; if it's a wedding, bar mitzvah, or Christmas celebration, you'll probably need room to dance.
Be sure to sign a contract for any banquet hall you book. This shouldn't be a problem, since the management will want to get paid one way or another. However, it also protects you from human error and fly-by-night companies that might "forget" about your event.
