Most submissions can be improved with proper audio optimization.
If you are looking for help with adding audio to your Flash, see this thread.
1. Convert to .WAV
You can import your audio in any format, although if you intend to loop it, we recommend .WAV format. Loops that are imported as .MP3s don't loop properly, and no one likes a crappy loop. See our list of Sound Converters to switch from MP3 to WAV.
It is fine to export your audio in .MP3 in your SWF export settings. As long as the loop source file is .WAV, everything works fine and nobody gets hurt.
2. Trim your songs
We highly discourage using an entire song unless you are specifically making a music video. If your game or movie isn't 100 percent dependent on the music, find a good loop that does the trick. A 30-60 second loop can offer a lot of audio variety and save a lot of size. The worst is when an artist imports a song that is longer than his or her movie. Their exported Flash file includes a three minute song and we only hear the first minute. Flash doesn't crop the audio unless you have it set to stream.
3. Avoid over-compressed voice recordings
One area where you shouldn't hold back is your dialogue. Find a compression point that allows the voice to sound clear and natural, rather than tinny and muffled.
4. Use music with permission
Avoid the use of commercial music; find audio that is royalty-free. We have our own community of musicians in the Audio Portal who are open to having their music used in your games and movies.
We love Radiohead videos as much as the next guy, but in general it is a waste of your time to make a video for an artist who is signed to a major label. The band may appreciate it, but their representatives usually won't understand the magic that is going on here at Newgrounds. Direct your creative energies elsewhere, otherwise you're just giving publicity to an industry that may not appreciate you. Why not give it to someone who does?