The Common Application: Download Forms
They ask the same questions year after year.
Still, there are other great ways to practice. The personal essay is about being personal, introspective, and analytical about yourself, so if you haven't already, consider getting a journal, where you can pour out all your thoughts. It's great practice, and it's fun, and private.
Another great idea is to read some great literature over the summer. Not only will it help with the verbal section, but it will help you with the essays--you can see how great authors have expressed thoughts in their writing. I'm reading Anna Karenina right now (Pevear, Volokhonsky translation) and I love it. Or you could read shorter works of literature as well. The idea is that you enjoy your summer while you're improving reading and writing skills. Edutainment! Oh, what a disgusting word!
But yeah, you don't necessarily have to answer the actual essay questions in order to get practice. I found it difficult to answer the Common App essays, so I made up my own: Tell us about something important to you. I found that much easier to write about.
You might also want to look at 100 Successful College Essays, which has a great selection of college essays that were accepted by many top universities and colleges.
Since you're headed to junior year, I wouldn't worry about it that much, but I think that reading a bit of good literature and poetry, and trying to write some good, personal stuff yourself will help. Just don't stress about it. Have fun!