The Prime Rule of Software Deployment.
There is but one rule that you need to remember if your job is deploying software. It is law, it is god, and you had best obey it if you want to simply your life.
There is no such thing as 100%.
You can apply it however you want, but it should be the first thing on your mind.
There is no such thing as a package/sequence that will run on every machine.
There is no such thing as a solution that will work 100% of the time.
There is no such thing as 100% reliability.
All good things to strive for, don't get me wrong. The point is not to rely on anything to be the "critical point". The one thing that makes everything else work. Reliability comes from simplicity. The more moving parts, the more likely it will be to fail, the more oddities will crop up, the more downtime you will have, the more work you will have to do.
It's easy to shoot for everything and the kitchen sink to provide awesome features to the client, or come up with an elaborate solution to a problem.
But bear this in mind. Duct tape is synonymous with fixing things for a reason. It's simple, it does a job, and very little can go wrong with it.
Find ways to make elegant and simple solutions work for complex problems and your life (and paycheck) will improve as a result.
Just some free advice inspired by a few recent questions.