Some key factors I strongly believe in that will lead to quick on-boarding
- Clear and good architectural design - that will help new engineer understand the blueprint of the software and rules/principle that need to follow
- Good code - easy to read, easy to understand, easy to maintain
- Clear Business goal/logics - help engineer understand the goal and direction of the project
- Mentorship - helpful colleagues, trainings
- self-driven /self-learning attitude: hire people that is willing to learn , ask questions and explore