I also just had my first intern. But I also taught at the college level and have had a few employees. A few suggestions to add to the already good lists here.

1. Tell them _why_ you do something.

This helps with cognitive load while learning, and helps them overcome some mental stress when investing in new techniques/methods.

2. Provide real code examples that work, and demonstrate them.

This is analogous to hearing a song played when learning to play a musical instrument. It's really hard to convert notes to music without knowing how it is supposed to sound first.

3. Be patient and ready to describe things from multiple angles.

I noticed I was more patient with people I have little time with. The more time you spend with someone the harder this gets. So be prepared for this.

4. You are likely to be wrong, be ready to learn yourself.

Every class I taught something slightly off, or made a mistake, or simply a student had learned some obscure thing from the internet that I had not learned myself. I learned alot by teaching others, but also by screwing up in front of an entire class. Be humble, expect to be wrong from day one, and be grateful when you are taught something new from anyone from any skill level.

Note: knowledge is easily attained these days, understanding why you use one thing and not another is not as easily learned. When an old experienced codger on the internet say to do something a certain way, take it really seriously and study why, then you can pass this on as well.