Make sure your signs can be read from a distance. That means large thick lettering (spelling counts!). Use short, blunt phrases on your signs to get your message across.
Know your subject matter. Whatever it is that motivated you to go out and protest should be your main message.
Take a large American flag with you to hold or mount on a pole in the ground near you--especially if you're countering an anti-war demonstration.
Be passionate, but not obnoxious. Be vocal, but not overbearing.
Speak the truth.
There's more, of course, but that's it in a nutshell. Hope it helps.
The DC Chapter's Warlord speaks with the wisdom of experience. Stay on message. Remain civil in your discourse (I always forget that one). Break off your discussions when they go circular. Use wit as a rapier.