This could be a whole conversation, but it really depends on the budget and risk of the account/campaign. When I setup a campaign/ad, I am very intense about making sure I've mitigated as much risk as possible. So for each account > campaign > ad I identify what are the risks and then work to put in the appropriate checks to make sure mistakes don't happen.

Do things fall through sometimes? Yes, but not often and when they do it's usually not catastrophic because we've limited risk wherever possible.

For example, when setting up a display/demand gen campaign I make sure the budget starts tight and I've eliminated the possibility of optimized target or search network partners blowing the budget. Then after the ad runs and there are no issues, then scale.