Protest bands come in many different genres and forms, e.g. Punk (Dead Kennedys, Black Flag), Rapcore (Rage Against The Machine) and Metal various songs by various bands. The general idea behind a protest and is that you have musical talent, and a message, and you feel that combining the two is a good way to get your message out there.
Step #1: Pick a Focus
One thing that is crucial is picking a focus for your band. By that I mean what you are going to "protest". Rage Against The Machine focused mostly on social issues, but they were not isolated to the U.S.A's issues. There were songs about South Africa and Rwanda, as well as injustice at home. Dead Kennedy's largely focused on issues in the U.S. and political issues.
Step #2: Musical Style
This is going to be mostly determined by what kind of music you like, but also consider what kind of lyrics you are writing, and what sound would fit with them. Metal, Punk and Rap are good types of music for protest bands. Metal and Punk generally are already big, mean and angry sounding, while with Rap, you can spit lyrics with speed and emotion.
Step #3: Lyrical Style
Again, this will largely be governed by your tastes, but here are a few guidelines. Your lyrics must make the listener want to keep listening. This is true with any kind of lyrics (obvious) but especially so in this genre, where the lyrics should be the main driving force in the song.
Don't be afraid to use metaphors, but don't bog the listener down with a speech. This is a song, here. The lyrics may look great on paper, but nothing is a nastier suprise than trying them out and finding that they are boring to listen to.
Sometimes, less is more. By simply letting the listener know what you are getting at, you can make a song totally blow someone away without using any words except names of third-world countries, and gradually starting to scream their names. Reads lame, sounds great.
Step #4: Stay consistent
In your songs, don't change your views from song to song. If you change what you are saying too much, it's hard to figure out what you are, a protest band, or a George Bush endorsment.
Hope this helped any people thinking of making a band, and if no one or hardly anyone is, I hope you enjoyed reading it. I enjoyed writing it.