How do you go about picketing a high school?

Answer:
Paint a piece of cardboard with your slogan, then nail it to a stick. Walk back and forth in front of the school. You are picketing.

Answer:
The first entry is the last step in the process. I'm assuming that the picketing is for the purpose of protesting something that you feel is wrong. If not, ignore the rest of this entry and go with answer one.

If you have a grievance at your school, the first step is to find out the source of the problem (not just what you or fellow students believe is the source); if there is recourse already in place that haven't been utilized; confirm that the grievance isn't based on an emotional reaction but a justified complaint; what steps should be taken that are not being taken to resolve the problem; solicit the support of any parents who also wish to see this problem resolved. Once you have done these things, you will be armed with the knowledge of what it will take to correct a situation and be better able to articulate your grievance; and paint signs that will have a better chance of delivering your message.