If a decision has not yet been made, ask the interviewer when he or she believes it will be made. If you have another offer, but would like to know about this interview outcome before making a decision, tell the interviewer. It may speed up the process. If you were not selected, try to find out what the interviewer would recommend to you that could improve your chances at your next interview. This is a non-threatening way of trying to discover why you were not selected, but also to provide feedback to you for future improvement.
Many organizations rely on second, or even third interviews, to make hiring decisions.
If you are chosen for a second interview, indicate your pleasure at being selected. Ask what the format will be for the second round. If you do not already have an idea, you can ask what the salary range is for the position before deciding whether to go further. Most companies that offer second interviews are very competitive with their salary offers anyway, so you don't need to ask unless it is really important to you. Wait to discuss salary specifics until the job offer is made.