1st Round - Group of 10. Introduce yourself and speak for 1 minute on a subject. Topic of subject varies for every round so it is pointless to memorize what they may ask you. However, one common question asked is definitely "Why do you want to fly with SIA?"
2nd Round - Certificate checks for everyone. Height checks will also be carried out at this point. If the girls seem to be slightly shorter than the requirement, you will be asked to do a reach test. You will need to stand about 1-2 feet from the wall, and reach for a taped line on the wall. Reminder for girls trying out, please do not wear too short skirts. On my interview, there was this poor girl, who was desperately trying to reach the line. Her dress was too short and while trying to reach the line, the dress rode up and well, don't think I need to explain what happened. So please remember, if you are slightly shorter than the requirement but is confident you can reach the line, don't wear short dresses!
3rd Round - 1 on 1 interview. At this point, a certain amount of luck is required. You will either get a helpful interviewer or a strict one. Mine was a rather difficult interview.