I believe the interview process starts when you submit a cover letter and resume. You may think that the interview process is over once you get a job. I disagree. To me, the interview is just getting serious when you get the job. From there, you’re typically on a probationary period as you acclimate to the company and they get to assess the skills you just promised them. Some companies have probations for just a few weeks while others can last up to a year. No matter how long your probation lasts, your entire probation is an interview. Typically, during probation you can be let go at any time. Many employers will give you a heads up if your performance isn't cutting it. However, when you’re on probation, an employer may not want to invest in developing you if there are red flags so early on in your employment.
Therefore, like you would during an interview, when you’re on probation you should be:
early;
prepared;
caffeinated;
polite;
friendly;
approachable; and
curious.
There is an expected learning curve for most new roles. If you show up ready to work, with a friendly attitude, and take the time to study up on whatever you don’t know about the work, you’ll be good to go. In sum, don’t leave opportunity for an employer to doubt you by letting your guard down early on in your employment.