Interview processes are quite varied both in content and tone. Some are laid back, others very rigid. Some have in-depth multi-day technical interviews, HR rep interviews and Captain's boards, and physical exams, while others are more of an informal chat. The thing to do is, apply everywhere you are interested and do diligent research on every interview to which you are invited.
IMO, the single most important thing a person can do at an interview is to be honest. You shouldn't air all your dirty laundry, but if you can't honestly explain to the interviewers why they should hire you, you should spend more time and money preparing yourself, then try again.
Accepting responsibility for your actions is an important aspect of honesty. Blaming others or external circumstances for a weak area never looks good to a potential employer. Find a way to accept some responsibility for any short-comings and explain how you've improved them.
Additionally, following instructions is very important. For example, if they ask you for your biggest weakness, and you tell them about something that used to be a weakness, but is now a strength (as some people advise), you are not following directions (or probably being completely honest, either.)
After careful preparation, if you are able to do the three things above, while being professional, personable, and friendly, you shouldn't have a problem with any interview.
If you're looking for specifics,
http://www.aviationinterviews.com/ has recent interview experiences for many airlines. (Free registration is required to view them.)
Good luck.