3. Ask Questions
It's a pretty cool opportunity to work with a professional in a career that you love - make the most of it! You get anywhere from 6-10 hours observing someone who does this for a living, and that's really cool. In all fairness, being friends with Mark gave me a unique comfort in talking shop with him, but the principle still applies even if you don't know your photographer that well. Step out, be bold, and ask questions! We're all in this together and it's important to keep learning as photographers. Don't grow stagnant.
4. Be Thankful
This one might sound obvious, but take the time to thank the photographer who brought you. You're getting valuable experience and (hopefully) great photos to add to your portfolio! That's a pretty cool thing, and an opportunity you otherwise wouldn't have had. So, Mark, if you're reading this - thanks a ton dude, I'm so grateful I got to be here. This was one for the books.
Any questions? Feel free to comment below - I'd love to talk!