I haven't been to an Army ball before. I'm a Navy wife and have been to Navy balls, Dining-Outs and Marine Corps Balls.
The first thing is always use your best manners in conversation, in the receiving line, on the dance floor, and when it's time to go. Of all the advice a person can give this is the most important. If there are things you're not sure of, your husband was given a tutorial in manners in his training. The two of you can go over this together so you both know what to expect of one another. For my husband, who was brought up in a well mannered home, there were some things at the table that he didn't know and was more than happy to share with me. For example, when you eat your bread roll; put your butter on the bread plate, break off and butter only one small bite at a time. This isn't how we eat at home, but it is how we eat in polite company.
The others are correct in that there are some ceremonials and a guest speaker. There are lots of traditions followed at these things too. Is this your husbands first ball too? If not ask him about how the order of the evening will go and that should help you. If it is (this is unlikely as he's probably been to at least a Dining-In to practice his manners training) then have him ask and find out about the order of the night as well as any traditions that will be followed. For us, we always leave when the smoking lamp is lit at the end of the evening. This is when cigars and cigarettes come out and we're not fans of either.
As far as dress goes, your husband will be wearing his dress uniform. You need to decide how the two of you will look best together. Find out what uniform he'll be wearing as this has been decided for him already by the command. I always go formal because he's in a tux (not everyone has or wears the tux dress uniform) and there's no way my man is going to out dress me! :) Plus, unless your man is a Medal of Honor winner you want the best thing he's got on his uniform to be the love on his arm. Then again, are the two of you dancers? If so, whatever you wear make sure you can dance in it. After all it is a ball. Keep this in mind when you pick your shoes too.
Most of all, this is meant for fun. And the others are right, this isn't the time to express your unhappiness at his repeated deployments or bad pay. Keep you conversation on the up side and NEVER gossip. You may even find spouses in attendance without their spouses due to IA, TAD, or God forbid KIA or MIA. Be sure to spend time with them and make them feel welcome and part of the family as it was hard for them to buck-up and come alone.
Usually there is also a memento for you to take home to remember the occasion. At all these events we've been to it's been engraved wine glasses; once it was engraved beer glasses. I love these things as they fill our cabinet over the years. They are cheap glass, but now we have a nice set of mismatched stemware. Now when we have a party everyone knows their glass by the engraving!
Sometimes there are photographers there. Get to the ball early in the cocktail hour and use that time to get your picture taken (your mom and dad will kick you if they don't get even a wallet size.). This is when your hair and make-up is at it's best so take advantage and record that expensive up-do! Over the years, it's nice to look back and see how we have changed. I think the most we've ever spent on this is $15 or $20, so bring some cash for it and the bar if you choose to imbibe.
So mind your P's and Q's and have a Ball!