Know what the SU can do directly
The Advice page is unusually clear on the important bits: the service is free for current SOAS students, independent of the university and external bodies, and impartial regardless of how the issue started. That matters when you need somebody useful, not somebody defensive.
The service says it commonly supports academic issues, complaints, housing and accommodation, money and budgeting, and welfare. If you are not sure where your problem fits, that is still a reason to start there.