Remember, folks, you're in a hostile environment. Not the Reagan Library, but in an even controlled by two media outlets that don't like you. Neither NBC nor Politico are fans of Republicans and they will do what they can to trip you up and provide sound bites for Obama.
Don't answer any questions that have nothing to do with presidential power. For instance, creation vs. evolution. The president does not have the power to decide which is correct and which is not, therefore anything you say on the issue can and will be used against you. Best answer, this has nothing to do with being president - move on.
Don't answer religion questions. It's none of anybody's business - move on.
Don't answer "raise your hands" questions. Refuse to respond and explain to the moderators that the issues are not that simple and they demand a fuller explanation. If they want to hear that, fine. If not - move on.
Keep the focus on the issues that matter to voters today - the economy. My guess is the moderators will do everything they can to keep the debate from being about Obama, jobs and the economy. Keep pointing things back in that direction.
It's not as important to bash each other as it is to remind voters that the current president is incompetent. You're in Reagan's house, remember his 11th commandment. Don't spend time speaking ill of each other.
Keeping all that in mind, have some fun. Anger is not attractive to voters but humor is.