1) There's detailed gouge on the internet, willflyforfood, etc.
2) Study the ATP question bank.
3) Know your Jepp's, especially big-airport stuff like taxi charts, SIDS, DP's, and the terminal area diagrams that big cities have.
4) Practice some IFR on a SIM or PC, holds, intercept, ILS. If you're used to small airplanes, you will need to be more proactive with the power. I did the 707 sim, but they use a different one know.
5) There will likely be a employee plant in your interview group, and the clerk at the hotel may be a spy...from the time you leave home until you return home, assume that anything you say or do is recorded for the benefit of the captain's board.
6) Assume that you will not get hired if you have any kind of medical history at all...day 1 is interview & sim, day 2 is an astronaut physical. Some poor kid in my group got canxed because his BP was a little high, and I mean just a little high...it was low enough that it didn't raise a flag with his AME.
7) If you get hired, complete initial training and IOE, then immediately start applying to other regionals. I don't think anybody from my interview group stayed longer than 6 or 8 months. I got hired elsewhere before my eagle class date, so it wasn't an issue for me.