There are several sources online http://www.sheldonbrown.com has a step-by-step process.

What I did was post an ad @ a lbs 'community board' offering to pay someone for lessons on wheelbuilding. Someone answered the ad and his teaching process was to have me build several front wheels. He had me dis-assemble them then put them back together w/proper tensioning by 'feel'. I had seven different old wheels. Some of them were steel rims which are much more difficult to true than aluminum. Anyway, when I could breakdown a front rim and re-assemble it in an hour properly tensioned, rounded and trued he let me go on to rear wheels. Several different types and spoke counts. Again, steel and aluminum w/standard gauge spokes.

So, he had me build and rebuild rear wheels w/dished and non-dished w/several different hub types. Some old SA IGH as well as 24 count hub/rim combos. He had me build sets w/2,3,4 and 5 cross. He worked w/me for over 3 months. I bought a Park TS-2 w/base to reward myself. He gave me a certificate that said I was a 'Bona Fide Wheelbuilder with Mad Skillz'. One of my prized possessions. It's on the wall of my bike room.

It was hard, tedious often frustrating work and I'd do it all over again and pay 5 times as much to ride/wrench w/t confidence I have today. It was like wheelbuilding bootcamp. One spoke not tensioned properly and he'd have me tear down all the wheels and re-build them. He charged me $150.00. Turned out we both an affinity for dark beer and fresh ground French pressed coffee. He's one of my best friends now.