The best tip I can give you is not to read to much into the negative comments of a few posters on here.
There are good and bad sides to every company.
You are only young and if you decide that bmed/bmi is the place to start your flying career then thats great for you and the company.
I don't know of many crew that have spent their whole career flying for the same carrier. If succesful, then you will probably try a few airlines until you find the one that suits you.
In the meantime, just be yourself at the interview. They'll want the real person in front of them and will soon see thru any facade.
The very best of luck to you.
LB !
