I went through the primary interview process very recently. If you are considering it yourself, my best advice is to be personable and as energetic as you can be. Most people that genuinely try and engage themselves will be asked back for a second interview. Make sure you pay attention as well, because I know they will ask you some questions about the presentation if you get asked back.

I applied online. They respond via email asking me attend an orientation and group interview in one of the selected cities. Mine was at a hotel in Austin. The group interview is basically a 30-minute teaching demonstration done in front of two interviewers and a small group (split in two from the original orientation group). We were given a lunch break in-between. After demos were over, we were given individual grammar tests. After that, the interviewers gave me a letter that said whether or not they wanted a one-on-one interview with me. The one-on-one took place the next day. Instead of a larger event-sized room, this was in an actual hotel room. The interviewer asked me a few questions about my experience and then asked me to give an on-the-spot five-minute (if I remember correctly) teaching demonstration using a random page from the textbook. The interviewer gave me some time alone to prepare beforehand--maybe around 10-15 minutes.