I've written a lot in the past about interviewing. I've had multiple careers and many jobs within those careers, so I have interviewed more times than you can count. Plus I've seen failed interviews. It never ceases to amaze me how people will show up and will be dismissed as an unsuitable candidate before they're even interviewed.
Definitely dress conservatively and as was pointed out, no perfume or nail polish. You are not allowed to have that as a CNA anyway, so that would definitely put you into the 'negative column' if you dress/makeup like you're going out Saturday night.
There is too much to state here about interviewing technique so I'll give you the 'highlights'.
Look at interviewer while speaking. A good interviewer will know some body language. Do not fiddle with your fingers, tap toes, etc. --- anything that would convey nervousness. Sit up straight, fold your hands, and talk directly to the interviewer --- no looking side to side, up/down.
It's very possible you'll get a 'personality test'. Answer questions honestly --- don't try to 'psych the test out'. These tests are designed to see if you're honest and 'suitable' for the job. You might think they are crappola, but the facility doesn't share that opinion.
Be prepared for direct questions. This is probably the hardest part, so prep answers in advance. You may well be asked:
1) Why should we hire YOU (which often gets interviewees flustered and they will 'hem and haw' an answer). What can you do for this organization? Plus, most of us are unconfortable tooting our own horn. Get over it! Don't be cocky, but be confident and formulate an answer that shows you want to learn, be helpful to people, make a difference, etc.
2) What do you consider your greatest accomplishment in life?
3) What do you consider your greatest failure in life?
4) Where do you see yourself in 10 years? More schooling? Go into
nursing? Go into admin?
5) How do you handle stress? What are you going to do if you are
working with an incontinent resident and someone else is crying for
help?
(Yes --- I have heard this question. You may well be 'tested' in what
you will do to react to multiple priorities at the same time).
6) Do you prefer to work with others as a team, or work by yourself?
7) Will you be able to make the time commitments needed to complete the
training and shift you'll be placed on. Can you work weekends? You probably know the 'standard' for this industry is to work every other weekend and some holidays.
Take a look at this. It's geared for business, but doing a professional interview has same components irrespective of the field.
http://www.businessknowhow.com/manage/impinterv.htm
http://www.businessknowhow.com/manage/impinterv.htm