Keep it simple.
Make it look good.
Give the Predators somewhere to hunt from, but also to return trophies too...
Keep the rules simple (you can walk the green stick and fire, run the red stick but not fire, you can fire this stick).
Give each side a chance of winning/losing quickly, but also how could they improve next time.
Best hand-to-hand combat system ever for conventions is 'Scissors/Paper/Stone' as everyone can play it. Don't put people off by having to look at 35 different tables to see if they hit, then another seven rolls to see if they kill!
Don't show any players the rules, be prepared to improvise.
Punish stupidity, reward bravery (it can be a very fine line).

I would endorse most of the above, in particular:

Provision of display material outlining the game being played and some background information.

Spare bodies who can field questions from the public and chat to interested parties.

A tidy and well-presented display - however modest.

Room for the public to actually see what is going on and, if they wish, to photograph said display.

There is room at most conventions for both the 6 x 4 "club" game and the monolithic bravura effort. It would be extremely boring if all games were constrained to a standard size. Above all, try for an original slant. Even the well worn, much played can be made fresh and new by a different viewpoint - the bitter struggle for Plancenoit on the flank of Waterloo; the 1915 Western front under a blanket of snow; the first battle of El Alamein with much dated equipment. And above all, try to use what you have - it saves a lot of frenzied painting.    

QuoteAnd above all, try to use what you have - it saves a lot of frenzied painting.   

This, this, a thousand times this.

So, what do I do every time we put a demo on...

Someone post that in thousand point type whenever I mention demo games