warn, worn

Warn or warn means to caution or alert to possible danger or harm--
The town requires that we post a sign to warn people that the road ends ahead.
The alarm will sound in time to warn the tenants of any danger.

Worn or worn ( rhymes with warn ) describes something that shows signs of use or handling--
It looks a bit worn, but it's still useful.
Your coat is starting to look worn. You should get a new one.
Worn may describe a tired-looking person--
She had a worn look on her face, and didn't seem to hear what he was saying.

Worn is also a past participle ( used with a helper verb ) of "wear", meaning to have on one's body, as clothing, etc.--
She found the jacket she had worn the night before, draped over the fence.
She was pleased to have the ring her grandmother had worn for so many years.

Now that you know that, you can say--
"I ought to warn you not to wear anything that looks worn to the interview."