Support the troops usually means actively aiding with money or actions. There are many organizations that make it easy to support the troops, such as USO, Wounded Warrior Foundation, and countless others.
Yep. Other things to NOT do:
1) Thank someone for his "service"
2) Clap, and cheer for the military floats at a parade
3) Rise in support of the military while people pray the national anthem at sporting events
You can avoid all of these situations.
For the first one, avoid hanging around douche bag military types.
Next, don't go to parades.
Finally, watch the sporting event at home, or if you're at the stadium, go take a leak, buy food, or get a drink of water before the prayer begins....
That way everyone around you will think you just happened to miss it, and you avoid getting into a fight with someone over your "diser'spektin' uhmyrrrrhah."