I interviewed with CO as well as AA (my current airline). In addition, I spent many years at Texaco interviewing people for new hire positions. Here are some suggestions...
1. Plan your travel to EWR to arrive at the appointed interview site
at least 30 minutes early--not at the parking lot,
at the interview room, 30 minutes early. They will have paperwork for you to fill out which will help kill the time. Being early or on time is a crucial part of the flight attendant job. Don't think that the interviewers won't notice (and make note of the fact) that you were there 15 minutes ahead of every other interviewee. They will.
2. Bring your own pen to the interview. In fact, bring two in case the first one runs out of ink. Make sure they both have black ink. Having the equipment with you to do your job is important. Your job that day is getting hired.
2A. Have a neatly typed resume with you. In fact, have more than one copy. This is crucial: Make sure all the words are
spelled correctly.
3. Be prepared to state clearly and comfortably in front of a group of people--either CO interviewers who are working flight attendants, or other interviewees, or both--who you are, where you live, what you currently do, why you want to be a flight attendant. As a f/a you will be called upon at times to ad lib a PA to a group of passengers for situations not covered in your standard PA book.
4. RE: Why you want to be a flight attendant. DO NOT, repeat,
DO NOT state that "I just want to work with people." It is a meaningless phrase. Unless you are a professional hermit, any job you do will involve working with people.
5. Make sure that if you are male, your hair is cut neatly, standard style, and above the collar. I don't care that you just flew a CO flight and saw a male flight attendant with a ponytail to his waist (just an exaggerated example!). He's already been hired, you have not. If you are female, hair either no longer than shoulder length or up in a bun. No extreme hairstyles. Both sexes, make sure that your fingernails are short and
clean. For women, clear or red nail polish. No, they won't care that green with glitter matches your dress.
6. Men wear a dark suit or a navy blazer with tan or grey slacks, white
long-sleeve dress shirt (there is no such thing as a short-sleeve
dress shirt), and a conservative tie. Make sure your shoes are shined and wear dark socks.
7. Women wear a conservative, well-fitted, but not tight, dress or suit. Hemline
no shorter than the top of the knee. A gold lame halter top and stretch hip hugger pants will make you stand out from the others, but not in a good way.

8. If you have any tattoos, make sure that they are completely hidden.
9. Above all else, remember that first impressions are
critical. There have been controlled studies that show that most interviewers make up their mind about an applicant--either good or bad--within the first 5-10 minutes of an interview. If the interviewer's first impression of you is negative, you're probably not going to get the job.
GOOD LUCK!
(Sorry. After all that typing, I noticed the original post date.)