About a year ago I started building bicycle wheels seriously as part of the Spindles project. I had built a wheel about 3 years ago for my own bike which was a very unsatisfactory process as I didn't have the correct length spokes and so had to cut my existing spokes to length. Since last year I've probably build about 16 wheels and so become somewhat more than a novice. I found that there are three very important aspects to wheel building: getting the right length spokes, gradually increasing the tension and awareness.
The right length spokes.
I have used a number of the web based spoke length calculators but the best one for me is Sapim as its very clear as to what should be measured and seems to give the right answer. I don't like the calculators where there is a drop down list of hubs or rims as the one I want is usually not there. I can use a vernier calliper (at least an electronic one) and have a steel 650mm rule to get the measurements required by the site. I've used DT spokes but have also started using Alpina plain gauge stainless steel as they come in boxes of 144 for about £20. I have a box of blue nipples that provides a single marker spoke for each wheel that I'm building this year. This is a trick I picked up from reading 'Its all about the bike' by Robert Penn.
Increasing the Tension
Many words have been written about the number of turns to apply when threading nipples onto spokes during the lacing process. I have found that to start, just screw the nipple up with fingers so that it's edge is just hiding the end of the thread is sufficient. When lacing the alternate direction spokes, if there is tension building in the wheel then slacken off the other spokes with a couple of turns. The aim is to have almost no tension in the spokes after it has been laced but all the nipples are at the same number of turns (assuming the rim is new and round). Hopefully this gets the radial position even and no 'judder' up or down as well as lateral evenness. At this point start to evenly increase the tension on each of the spokes using the 'key' spoke as a guide. The best spoke keys are produced by Park.
The most important aspect of wheel building is being focused on what is happening. Don't try to lace too quickly as mistakes are time consuming to rectify. Go at a pace that allows the mind's attention to easily follow. Don't listen to music or get distracted, just stay with the building of the wheel. Focusing the mind is the most difficult thing but can also be the most rewarding. Building wheels is almost a meditation practice: as the tension in the spokes is slowly built in the wheels so the tensions in the mind are released. Before you know it the wheel is built.