Hello Blacker: I see this is your first post here on PC. So... welcome to Psych Central. Thanks for bringing your concern here.

You asked how to have a stable performance when you're not on a good situation during an interview. I'm not sure what to tell you about this. I think one important thing, with any job interview, is to be prepared. Learn as much as you can about the job you're applying for as well as about the employer & the type of business they are in. The more knowledgeable you are the better you are likely to come across & the more confident you can feel in your ability to do well in the interview.

Beyond that, if your situation is one of trying to do well in an interview while you're struggling with depression & anxiety, that certainly does complicate everything. I don't know if there really are any tips I can offer on how to do well when one is struggling with mental health concerns. I think what may perhaps be necessary would be to treat the depression & anxiety before you get to the point where you have to figure out how to do well in a pressure situation such as a job interview. If you wait until the last minute, so to speak, it may simply be too late to do much other than to just forge ahead & do your best.

Having written that, however, here are links to 3 articles, from Psych Central's archives, that offer suggestions for how to do well in a job interview plus one that talks about how to deal with job search rejection:

NLP Tip: How to Ace that Job Interview | NLP Discoveries

In Job Interview, Focus Less on Anxiety, More on Warmth, Assertiveness

5 Body Language Tricks to Ace Your Next Interview

4 Ways to Deal with Job Search Rejection

I hope you find PC to be of benefit.