Yes, I admit it... I'm an artist and I have lots of nail holes hiding behind my wall hangings!
I definitely disobey the number one rule which is, DON'T EYEBALL IT! Yes, break out the measuring tape, do some math and get it right the first time.
There's a method of tracing your frames on paper and then taping them to the wall to see where you want to end up. I haven't done this yet, but I think it's a great idea and I will use it the next time I curate my spaces.
An extremely important rule to follow is to use the proper tools when hanging on drywall. I've been replacing nails with screws & drywall anchors. Check out Amazon for some inexpensive kits.
I recommend stocking up on useful tools that will make your life easier, and keep them in a bin at the ready.