I’d add two common DIY code-related mistakes to your list:

~ If you’re using plastic boxes, the tabs where the wires go in are NOT supposed to be taken off in the same way that you knock out a hole in a metal box; they’re supposed to stay in place and serve as your wire clamp.

~ Be careful to not take off too much of the insulation/ sheathing, since it has to extend into the box by a half-inch or so. If it doesn’t quite reach inside the box, it’s not to code.

(This one courtesy of the previous owners of my house who put in the bathroom light with almost a foot of the sheathing removed outside of the box, which means that I now have to strip out a huge section of the drywall in my bathroom ceiling to bring it up to code if I don’t want to add in an ugly j-box. Oy!)

Several safety additions:

~ Check the power every. single. time. Never trust that “no one would have turned that breaker back on while I was eating lunch.” Never trust that all the wires in a box are on the same circuit if they’re not connected together. Never even trust that the top plug in a receptacle is on the same circuit as the bottom one (I got a nasty shock from that mistake!).

~ When you turn a breaker off, tape it down to ensure that anyone else looking into the panel knows that it’s supposed to stay off. And if you’re working on the wiring for a switched light, tape the switch down even though you’ve turned off the breaker at the panel.

~ Take the time to take off your rings and put on rubber-soled shoes if you’re going to do electrical work.

Two convenience additions:

~ Do yourself a favor and grab a permanent marker and write (in the box, on a wire, on the back of the plate, on some special wire labels, somewhere!!) which breaker controls the wires in that box. Even if you have a very clearly marked panel, it will cut down on the time needed to search for the right breaker.

~ Also, mark where each wire comes from/goes to, so that you can trace the wiring path long after you’ve misplace the diagram that you swore you’d always keep handy.

And finally, one frivolous addition:

~ If you have a wall open for any reason, grab some permanent markers and let friends, family and especially kids go to town on whatever’s behind the wall - draw pictures, write your names, write something about the renovation you’re doing, stick in some photos or news papers, create your own little time capsule. Old house owners generally LOVE finding hidden things behind their walls, and you may totally make someone’s day 50+ years from now when they need to open up that same wall that you’re putting up now.