The peepul say to stand up tall, with your shoulders back, to look tough and confident. Here is my example of good and bad cat posture. This is slouching:
This is sitting up straight and tall:
It's a combination of doing the following, stretch your neck up, straightenyour front legs, hold your head high and most importantly, don't forget to suck in that furchin.
If I were going to a job interview (I don't know know why I would need to do that, I have an easy pampered life). This is how I would sit to talk to the boss.