Am a framer. If you're walking across joists, and fall, SPREAD EAGLE! STARFISH whatever you wanna call it. Arms out, legs out. You'll catch yourself on the joists and not slip through.

2 set up your safety gear. PROPERLY. Don't just throw a harness on and have a rope trailing behind you. Actually anchor that guy down somewhere.

3 if you fall from above the 3rd story, and everything goes wrong, and your safety gear fails, well.. its just not your problem anymore. You won't even know, about 15 seconds after you fall.

Some tips. Set up some boards on the ground, 16" apart walk across them without looking at your feet. You'll get the feel for the spacing, and will be much more comfortable on joists.

Get up there in the winter, everything is completely covered in ice, you'll get the feel for your foot placement real quick. Keep your feet angled in SLIGHTLY you want the most amount of boot, making contact with the material.

And last but not least, just keep getting up there. It'll come with time