This will at first blush seem counterintuitive but trust me it is definitely ONE of the actions that all people with successful launches do (even if they don't know it)
And that is have a "zero sales plan"
What is your plan if there are zero sales?
The reason I say this is key is because it happens to all of us and what sets the successful launches apart is that we pick right back up, look at what worked, didn't work so well, etc. and get back into the game fast.
I'm equally as adamant about having solid launch strategies and you'll get LOTS of great advice/tips/opinions/etc. but what rarely gets mentioned and what I know works is that you have to have the plan for the "worst case scenario" (I'm a lawyer so I've been planning for worst cases for a long time :) ) and planning for those worst cases is what makes for lots of best, best cases.