Keep a notepad & pen handy so you can write down names & titles of people (with a physical description, if you’re horrible at names like I am) as well as notes about where things are kept, processes to follow, tasks assigned, promises made, etc. The other tips above are all good: be friendly, wear a smile, do your best even on the trivial tasks, chip in wherever you can, ask how else you can help, ask if you can learn about [something you’re interested in but haven’t been told to do], at the end of the week, ask for feedback on how you’re doing & how else you can help. Non-profits love motivated, energetic people who are really trying to make a difference. This could be an important job reference for you, so keep that in mind (especially when you get asked to do something that seems very minor…the attitude is more important than the responsibility at this point).