Doing this currently:
- Assume they know nothing, what is obvious and routine to you is probably brand new to them, or they might have had a 2hrs module about it in college, but basically zero experience (that's why they're interning)
- Give them the most simple task at first, but something that make them use your workflow (read ticket, change ticket status, code, test, commit, PR), this is already a lot for them to digest
- Include them in your project stand-up
- check-in once or twice a week, maybe a little more at the beginning. Send a DM at the end of the day to see what's up, no need to call all the time
- Do some pair programming, show them stuff you work on, show them you working on stuff
- Introduce them to colleagues in meetings, make your colleague introduce themselves
- Make sure you give them a task that interest them, or show them why this is an important task
- Make sure not to time pressure, they're learning and cheap, can't have it all...