I am a first time builder who is about 75% of the way through my 12iS.
I agree with everything Patrick says. I will reiterate his line about the steel flapperon counterbalance tubes. There are jigs for holding a drill bit in place when drilling into curved surfaces. I would recommend using one of those (the problem is the steel is so strong and the skin is so thin it's easy for the bit to walk).
A few other points to consider:
If you can afford to do so, a builders assist like the one from synergy air is very valuable. My wife and I took the class together and finished the empanage in less than a week. http://synergyair.com/builder-classes/empennage/
Spend the $10 and add the electronic version of the plans *every* time you order the next kit. You'll get the most up to date version of all the sections. I have this on my home laptop and my work laptop. Conservatively I read each chapter 10 times before I start doing anything - and I *still* make mistakes
You can put spare time at work/home to productive work by reading/rereading the plans before you put your hands on any parts. As many have noted prior, a less than 100% clear drawing on page 3 can be clarified by the drawing on page 10.
Cleavland is great beyond just selling tools. They have a great set of youtube videos on how to use their tools. Watch those videos. Also EAA Hints for Homebuilders - watch as many as you can stand
You can get deals on used tools here:
I bought my 90 degree drill from there and also managed to snag a #30 reamer that's about 1" long. My tech counselor was impressed I was able to snag that baby. Also: ebay.
Join local EAA chapter and get connected there if you haven't already. Most valuable decision I've made so far. I have a regular work partner who has already built a 12. His experience (AP/IA with 35+ years work experience) cannot be quantified. Paraphrasing my father: "his pinky knows more about building airplanes than I will ever know." Hopefully like me you'll get both a willing helper and a great new friendship.
The other valuable thing I did was read a builder's blog from start to finish. I found this one:
there may be others now devoted to the 12iS. These are a great supplement to the plans.
I actually built a 4x8 table on rollers. It has ~3.5 foot extensions hinged at each end. It's large enough with those extended to hold the wings while you are putting them together. I also built two EAA tables - they hold my stationary tools and sorted parts from the various kit paper bags.
One more piece of advice. From my tech counselor: "do it right the first time." It may seem trite, but I hear those words every time I screw something up
If you aren't sure you can squeeze, or reach to pull a rivet stop and get some help. Pulling a 4-3 rivet correctly takes 1-2 seconds. Drilling out an improperly pulled or squeezed rivet takes considerably longer. The longer you build the better you'll get at knowing when you should stop. Error on the side of caution at the beginning.