First and most important step is to get all your admin absolutely spot on - otherwise you will be turned away at the door.
A fairly short interview with a couple of management pilots then a free go in either the B744 or B777 sim. Normal take Off, SID, steep turns, STAR, ILS Land. Another take off, V1 cut, around the pattern. Land. If all went well on Day 1 you will be invited to stay for the medical on day 2.
I would not recommend SIA Cargo as an F/O expat position though. No real possibility of command, expensive cost of living, especially if you have children and there are much better F/O positions available elsewhere.