Any advice or helpful things to have for someone going into an audition for an Army band?

Without knowing your level of playing it's hard to give advice. Here are some basics.
1. pure tone through range of all notes and dynamics
2. be able to balance and tune with those around you
4. timing must be steady
3. be able to read level 6+ music.
4. articulation should cover all ranges of tonal communication
5. have command of full range of notes
If you have all that, you're ready to prepare for an audition.
The audition (AMPA) has 3 parts.
Part 1 = ceremonial music. You'll be asked to play our National Anthem, and other ceremonial pieces
Part 2 = you will be given 5 minutes to display your technical skills, lyrical skills, and a third skill all on your primary instrument by using exerpts from solos, etudes, studies, etc.
Part 3 = quickly prepared music. You will receive a pack of music 24 hours before your audition. You will be expected to learn and perform the packet of music for your audition. This is called...wait for it... "quickly prepared music". This music will cover the range of abilities expected. There will be 6 to 9 pieces to work-up.
That's about it. Good practice!

This question has been sitting around. My observation of various bands, or other specialized small units has me seeing the same things. Skill, teamwork, and do they like you? You'll be more than visible so you better look sharp and not have an inner tube. Be prepared to sit in and do some sets. Be approachable. Be cheerful. Be interested. Be honest. Be flexible. Like anything else, they're looking to see if you're a good fit and they're better off with you than without. Also, get a good idea of what you may be getting into. "Band" is generic. Most MIL music outfits have various sub groups within the overall "band". A jazz group. A drum, fife, bugle group. A vocal accompanied group. Given all these configurations, a member's schedule can be more than crazy. Since the billets for musicians has been cut, the workload hasn't been cut as much. So the area of coverage is larger, travel longer, etc. TDY money is tight, hence you may drive 8 hours to do a gig and have to turn around and do 8 hours to get back to your rack. But consider doing that cheerfully if it means a SM gets a proper send off, or welcome, or final Taps.

I recently joined the 395th Army band and the audition goes like this: cerimonial, prepared, short-notice music. The biggest thing is to prepare prepare prepare. If you double on any instrument, bring that and play it too. If you can sing, that also adds points. If they let you, stay all day and drill with them (ie. rehearsal) and have them get a feel of how well you work with others. Good luck!