I say some stuff with a Lets Play:
* Make sure we don't show everything, cause then they have stuff to see (so I think no campaign)
* Don't show to much at once, cause it's easy to lose a viewed with "food, population, power, common ore, rare metal, chassis then turret"...
* Try to show both sides in a game, like the Eden Star ship colony mission
* Don't mention any flaws with the game
* Maybe show a fan based custom map, like survivor, which might be a really good one since it shows almost all basic elements of the game
* Don't use hotkeys, since the viewer can't see the keyboard