I have a few that I wish I knew when I started.
Buy a cheap multimeter. It’ll come in handy often, especially the connection tester mode
when probing for bend points, have a small resistor in between your probes (~100ohm). That way you’ll never actually fry anything, just the resistor. Really sucks to ruin a keyboard while looking for bends, but burning up a resistor is no problem
SHRINK TUBING. Not the adhesive kind. Great for cable management, covering joined wires, & making those switch solder points extra secure.
You can find some pre-assembled 555 modules online for very cheap (like less than $2 a piece) that are surprisingly useful in bending projects. Connect the output to some random PCB points & see what happens. Most have built in rate & cycle trim pots you can remove & wire to normal potentiometers for easy speed & shape control