The #1 rule I have applied over the years is to keep IT management as simple as possible.
Now we all agree that simple means different things to all of us, so what I'm referring to here is to as far as possible strive to ensure that you can standardize as much as possible, automate whatever can be automated, minimize all dependencies and use the right tools to proactively obtain insight into the state of your IT network.
In other words, as they say, even when it comes to IT, less (complexity) is more (uptime and security). So for example, perhaps the next time you're looking to switch your routers, make sure to get them all from the same vendor and as far as possible specify and maintain the same base configuration across all of them, and do monitor them as well.
This one rule has saved me substantial headache and time and I'm certain it'll help you as well.