The answer is, I didn't. I was always a libertarian, I just didn't know there was a word for it. I didn't know there were more than 2 choices in politics. 
When I was 19 I was in a pop punk band, we sang about girls, and dumb stuff like crickets and the person who invented shoes. I had only been on my own for a little over a year but I was starting to see the world for what it was. What I saw was a world where others get together with those who agree with them and force their will on those who do not. 
I was always an outgoing person, and I've always spoken my mind, but I'm at my best on stage. My goeeful demeanor off stage is replaced by a serious and energetic demeanor on stage. My pop punk days were over and I had to tell the world how I felt. As the new band formed, the lyrics I was writing reflected my new view of the world. Our singer had a similar view and his lyrics followed that same path. We wrote about Columbine, heroine addiction, abortion, and our view of government vs freedom. 
At that time I thought I was a Republican. They were about freedom, small government, low taxes, and had my parent's vote. It wasn't until I walked into the voting booth in 2008 until I realized I had so little in common with Republicans that I couldn't vote for them any longer. That was the first time I voted for a 3rd party.
I still didn't know what a libertarian was but I knew I wasn't Republican or Democrat. It didn't take long for me to realize what a libertarian was after I joined the Army. I very quickly realized the monster that was government. Endless red tape, waste, fraud, and abuse of taxpayer dollars. Not to mention the brothers I personally lost to a war that we have no business being in. 
By the time I was out of the Army I was staring off the cliff that was Anarcho-capitalism. Finding that there was no solution to any problem that could be solved by government. I was reading Ron Paul, Murray Rothbard, Thomas Sowell, and every libertarian thinker I could get my hands on. Now I find myself a member of the Libertarian Party. The poor punk rock kid from Waco, Texas. The guy who was saying it before he knew what it was. I'm an individual, I'm an idealist, I speak up and speak out. I am a Libertarian. 