School is the only way. If you didn't major in philosophy in a good program, chances are you're not very good at it. Even the exceptions, those that studied philosophy at so-so philosophy programs, aren't as good as those who benefited from a good philosophy program.
The rest of you simply aren't very good at philosophy at all. The topics of philosophy are ultimately what separates philosophy from non-philosophy, but thinking clearly is the actual skill. So, I'll say it again: most of you aren't very good at thinking clearly. It's a skill. That's what most people don't understand. It's a skill you must practice, practice, and practice. Going to school for philosophy is like being an apprentice. You hone your skills under the tutelage of a master, and it's the master who will help you become a master too. The reason why people who don't major in philosophy tend to be such weak thinkers is that they never have the benefit of the tutelage. Usually, they also acquire the attitude that they don't need such tutelage, that they're strong thinkers already, or that there's no authority when it comes to philosophy.
Don't take the advice of people who aren't good at this stuff. If you truly want to become a philosopher, go to a school with a decent philosophy program and take classes. Write philosophy papers. Lots of them. Have them corrected by a philosopher or someone much better than you at philosophy. That's how you'll improve.
"Some people would rather die than think; in fact, they do so" -- Bertrand Russell