While belonging to the latest social network is always a good idea, and Facebook and Twitter are the current juggernauts for broadcasting content, you should always have a landing strip for your content. I would recommend a well-designed Wordpress or Squarespace. Then, post, tweet, link, share your content from your website. This will drive traffic to one location instead of confusing potential editors or colleagues to which place to go to find all of your work.
Just get started already. (What have you done for me lately)
Seriously. Stop reading this, and get off your butt. Or, hopefully, you're reading this on a mobile device while working. Nothing replaces hard work. Often, students think that they cannot be respected as journalists without a degree. Wrong. As long as you continually produce good journalism, age or experience will be less and less of a limiting factor in your career.
Again, nothing replaces hard work. Journalism is a field that is not only highly competitive between colleagues, but your success is dependent upon the connections you make. The only way to make those connections is by practicing journalism. Thus, it's a pretty simple equation; the more you work, the better you get and the more people you meet. This will result in better assignments for bigger news stories. Period.
Find a mentor
Your advisors are great, your professors are experienced and your mother loves you (still fact check that), but you need a professional - someone you can call when you need to figure out a day rate or when you need advice on contracts. Mentors can help you find that first big job and can know you well enough to tell when your work is slipping.