My approach is to learn the stack (read books, sketch/prototype).
Get the team to whiteboard the architecture with you. This is better than existing documentation because you will get the full commentary and start building a mental model of the software.
Ask the team about problem areas.
Don't push on major stack/architecture changes until you know the stack/architecture.
Make sure the base engineering practices are there. You should have a seamless workflow from pre-merge code reviews, testing, and deploy.
Get the team to whiteboard the architecture with you. This is better than existing documentation because you will get the full commentary and start building a mental model of the software.
Ask the team about problem areas.
Don't push on major stack/architecture changes until you know the stack/architecture.
Make sure the base engineering practices are there. You should have a seamless workflow from pre-merge code reviews, testing, and deploy.