I did not see this before but it sounds like your first experience was not too bad. It gets better with practice!
You actually don't need another person; I do mine myself. I also do it outdoors (nice in the spring, birds can make nests with your hair).
I have long wavy, thick hair so I straighten it before I cut it. Cutting wet hair is risky for me so I like to do it dry.
Tools: Only one! Hair shears. You absolutely need hair cutting scissors, everything else will hack up your hair. They are inexpensive and last forever.
I also use a table mirror since I'm doing it outside.
Bring all the hair to the front, evenly parted down the middle.
Cut as much as you want, in a straight line. For thick hair it helps to divide hair into more sections (2-3 per side). You are now finished!
For layers, I just divide my hair into sections and cut at an angle. This graphic helps some although I do not do all of the steps. :)