One can simply read law textbooks and judgements of legal cases, but what else?
If you simply want to acquire knowledge in law, reading is the most effective way.
Even law courses (at least where I am from) consists of tons and tons of reading. Read, read, read. Usually the items are:
- Legislation (i.e. the actual law). If you are attending an Intellectual Property class, you will be assigned to read Copyright laws. In a Criminal Law class you will read the laws about prosecution, and legal definitions of various crimes.
- Textbook / lecture slides. They will provide a laymen explanation of the concepts and terms you come across in the legislation, along with simple examples.
- Legal cases. These are especially important in a country where Common Law is in practice.
Here is a fact: you cannot learn every aspect of law. There is simply too much. That is why there are lawyers who specialize in contract, accident compensation, land dispute, etc.
In the states of California, Maine, Vermont, Virginia, and Washington, an applicant who has not attended law school may take the bar exam after reading law under a judge or practicing attorney for an extended period of time.
In 2013, 60 people became lawyers this way out of 84,000 via law schools.
Ignore the other answers--they are emblematic of what's wrong with the law today.
If you want to understand the law, you must understand what the law is for: it's not to create lawyers.
Learn what the American Revolutionaries fought for. Read the Declaration of Independence and get in touch with the Spirit of the Law. The Pledge of Allegiance also has it.
Because of the common values in mankind, there are only two pillars of which the entirety of law rests: Liberty and Justice. Understand those, master dialectic and you won't need a degree.