hey, i didnt get a SA position my first year, but had some friends that did. They didnt do anything to prepare. I have an SA position for this up coming summer. I think its more of a training sort of program. My buddy, as a 1L, wrote memos, did entry level work, etc. However, they have to realize that as a 1L you have very little practical experience. Even as a 2L, I have little real world legal experience to where I can contribute anything without a little instruction first. They have that mentoring program during the summer that provides some instruction into what is required. I think they take time to train you and provide enough feedback so you can do good work for them. I wouldnt stress it or do anything outside school to prep for it.
Congrats by the way.