Onboarding is one of the critical steps for any new person joining the org.

For the intern

Don't worry about sounding stupid. Ask as many questions as possible initially.
Make sure to get clarity on what is expected from you on first day, first week , first month and first three months.
Try to document all things you do. This will come handy for self analysis as well as updating to your mentor.
Send a daily, weekly and monthly update to your mentor.
giving and taking feedback is very important please do it.
answer https://vote.neubitat.com/p/challenges-of-interns
Pick something from https://micro-tasks.learningpaths.io/ and start working on it
What is your audacious goal and What is your biggest fear
read about the thumb rules I follow meta rules|meta rule. most people at learningpaths/Learning Paths|Learning Paths and neubitat also follow this. recently started the same at vegrow as well.

For the mentor

Make sure onboarding is smooth.
Allow the interns to make mistakes, own up and learn.
Don't spoon feed everything. Give them opportunities learn, figure out and own things by themselves.
Establish boundaries and thumb rules so that they know what is expected out of them.
giving and taking feedback is important. please do.
anwer https://vote.neubitat.com/p/issues-for-mentoring