What Specifically Can I Do To Become Professionalized?
In one sense or another, everything that can be considered professional development is also part of your personal development. Personal development involves undertaking activities and fulfilling responsibilities which expand your life experience and help you to become a mature, well-rounded, knowledgeable, and ethical person - exactly what professional programs, internship directors, and employers are looking for.
But in addition to the other professional development endeavors described throughout this web site, other, more simple endeavors and experiences can also be part of your personal development: consistently reading daily newspapers, magazines of substance, or alternative news sources; reading fiction; pursuing hobbies and other extracurricular interests (rock-climbing, photography, dance, sports, travel, writing - anything fulfilling that makes you a more worldly person); attending university and city-wide academic, cultural, and other events; being mindful of personal challenges you've overcome, or mistakes you've learned from. In other words, develop and maintain a strong sense of intellectual curiosity throughout and beyond your undergraduate experience.
Following from these examples, admissions committees and hiring committees often look for something interesting that sets one applicant apart from another, or which might make the applicant an interesting addition to the classroom or workplace.
At least as important, if not more so, is that activities of this sort are simply a fulfilling part of your educational process and your ongoing experience as a life-long learner.