I was interviewed for a US tourist visa last year. Just a reminder, you will only be approved if you have strong ties in Qatar to convince them that you will be back. Examples of strong ties would be:

1. Your job -- I think applicants handing supervisory or manegerial post has stronger appeal than ordinary staff

2. Your family -- Singles have lesser chance to get a visa than married ones (They might assume you might tie your knot while in there)

3. Your length of stay in Qatar -- I think people should have long years of stay here as a strong tie qualification cuz if you have just been here for a few months or years then they might think you are just country-hopping and would never leave US

4. Your finances -- Show them you have enough fund for your visit and that you also have savings. Land/house titles would also help if you have some

These things would be in the first set of their questions and if they think you have a loophole in any of these 4, then they might give you the doomed "DENIED". Do self-analysis of yourself and those 4 criteria.

For the interview, just be confident in answering, don't stutter and be straight to the point.

Good luck ;-)