What should I take most advantage of at my writing summer programs?

This will be slightly different advice than others will likely give. I would pay close attention to what everyone else is writing and saying. It's a good way to get ideas about construction and approach, as well as a way to see what mistakes others make or improvements they could make that you can learn from. The idea here is that if you focus purely on your own work, you not only deprive yourself of ideas, but you limit your experimentation only to what you yourself can produce. Being surrounded with other experimenting and learning writers is an idea opportunity to expand your experimentation significantly.

You definitely take advantage of the feedbacks you will receive from your professor. It will help you hone in on your writing skills. Besides practicing writing and getting feedbacks, reading (a lot or as much as you you can) is also a great tool to improve your writing abilities.

Best wishes to you Emily!

For creative writing, I'd recommend 3 things:

1. Read a lot -- of published authors -- and discuss what you've read with others to exchange ideas about what theses writings. What did you/they like, what wasn't so great. I'd expect you'll hear different opinions because people have different tastes. For me, reading a lot helped expand my vocabulary, expanded my understanding of story, and helped me discover beautiful writing.
2. Read as much as you can of what other attendees write. Offer feedback when it's wanted or as appropriate. You can learn a lot from seeing the writing of others who are learning as you are. I've learned a lot that way, and also learned about writing by making the effort to critique (again, in a helpful way) the writing of others.
3. Write a lot, and get feedback on your own writing. That's sometimes hard to bear for some people, but constructive or well-meant critiques can be extremely useful to help you improve your writing. I've been in writing groups where the feedback has been instrumental in helping me hone my writing skills, and I've had professional editors help me raise the quality of my writing.