What I learned the hard way
Every rule on this page cost me something. That's the difference between a rule and an opinion. Nobody writes these down until a machine has already made a fool of them, so here are mine, paid for in full, so a few of yours can be free.
None of this is about being clever. The people who run good home setups aren't smarter, they've just been burned in more specific ways and kept notes. That's the whole edge. So here's the notebook.
The network doesn't tell the box it moved
I typed a fixed address straight into a machine because it felt tidy. Then the network changed underneath it, and the box kept shouting its old address into a room that had been demolished. It looked dead for days. The hardware was fine the whole time. If a device needs a permanent address, the router assigns it, because the router is the only thing that knows when the map changes. The box in the closet never gets the memo.
The part you suspect is usually innocent
When something's slow, the human instinct is to blame the biggest, newest, most expensive part. It's almost never that part. My "slow server" was a routing mistake sending traffic the long way around. My "slow database" was a query reading far more than it needed. Stop guessing and go find out what the data is actually doing. The bottleneck is almost always somewhere boring you didn't look, and the fix is usually small once you can see it.
Investigate before you touch. The urge to start changing things is the enemy. Ten minutes of finding out what's really happening beats an hour of confidently fixing the wrong thing and creating two new problems on the way.
Most automation isn't worth it
I've spent an afternoon automating a thing I do twice a year. The script took longer to write than a decade of doing it by hand would take, and then the script broke and I had to learn it again to fix it. Before you automate, ask whether the task is really a thirty-second manual action you do rarely. If it is, leave it manual. Automation is inventory. Every clever script is a thing you now own and have to maintain forever.
Match the ceremony to the risk
Not every change deserves the same care. Flipping a setting you can flip back in five seconds needs no ritual, just do it. Wiping a disk, changing something the whole house depends on, or anything you can't undo deserves a backup, a written note of how to reverse it, and a slow hand. Treating a reversible one-liner like surgery wastes your life. Treating surgery like a one-liner is how you lose data. Spend your caution where it actually buys you something.
The rules, pulled out so you can steal them without paying for them first. Pin these somewhere you'll see them before you touch a machine.
1. Reservations go in the router, never on the box
If a device needs a permanent address, set it as a reservation in the router, keyed to the device. Leave the device on automatic. The router knows when the network changes. A hard-coded box does not, and it will wait forever at an address that stopped existing.
2. Investigate before you touch
Before you change anything, find out what's actually happening. Read the logs, watch the traffic, measure the slow thing. The fix you land after ten minutes of looking is smaller and righter than the one you guess at in the first minute.
3. Suspect the boring part
When it's slow, the expensive component you're blaming is usually innocent. Go measure what the data is really doing. The bottleneck hides somewhere unglamorous, and you can't fix what you refuse to look at.
4. Don't automate a rare thirty-second job
Ask if the task is really a quick manual action you do rarely. If it is, keep it manual. A script you have to maintain is a liability, not a win. Automate the things that are frequent, error-prone, or run while you sleep. Leave the rest alone.
5. Match ceremony to risk
Reversible and small: just do it. Irreversible or load-bearing: back it up first, write down how to undo it, move slowly. Put your caution where a mistake would actually cost you, and stop spending it where it won't.
None of these are clever. They're just the notes from the times a machine won, written down so it wins fewer times against you.