Reading books, talking to experienced investors, forums like this, podcasts, seminars (I don't recommend going to the expensive one, not in the beginning), going to a local real estate club, etc.
I worked for other people who were doing what I wanted to do. Put in sweat equity, gained knowledge, and got paid for it.
Go in with the mindset that you are never going to know everything about Real Estate. With that being said, read books, listen to podcasts, attend a couple of REI meetings and network your way into some kind of mentor ship if possible.