Building a prototype rig with naked boards and wires (running 24V, 3.6 A): how to be safe?
There is a whole body of knowledge about how to keep from getting zapped, and I'll give you a few highlights.

1) At 24 volts, if your skin is dry you won't feel more than a tingle. Don't play with electricity in the rain and don't spit on your hands before you start trouble-shooting. Go back to the Wiki article and you'll see that the 500 ohms figure was for wet or broken skin, so don't let live wires stick into any open wounds you might have.

2) If you're seriously paranoid about getting shocked, put the circuit in a box with a switch attached to the lid, so if the lid is opened the power is turned off.

3) Poking around a live circuit is normally necessary as part of troubleshooting. First, make sure you're sitting or standing surface is dry and not conducting. Second, keep one hand in your pocket at all times. (I'm not kidding about this.) That way, you cannot make a circuit from one hand to the other. At 24 volts, this is generally unnecessary, but it's a good practice at higher voltages.

4) Never build a circuit which is directly connected to the AC power lines. Always use an isolated power supply.

5) Note that there is such thing as a "let-go threshold". When the power is on, you can poke and prod with a probe to your heart's content - just don't grab anything. Again, at 24 volts, this isn't a problem (unless you're violating rule 1 and playing in the rain), but it's still a real good policy. If you see a loose connection, or a screw that needs tightening, stop and turn off power, then fix the problem.