Read every book you can until you realize that most of them were written by some fairly lame authors. If fact, most books are probably written by ghost authors who write a book for some wannabe expert and the ghost writers get ALL OF THEIR INFORMATION from other lame books. But, many books have maybe one good piece of advice.
Math is super critical. There are many investors who don't understand and can't do basic math. Knowing how to do simple algebra, calculate the return on investment, create spread sheets, etc. is critical. If you can't do the math then you may have to make decisions based on wild guesses and other lame investors advice. I would not make an investment if I could not do 100% of the math by myself.
Go to every real estate club meeting you can attend. Again, there are a really lot of serious idiots including really lame brokers who don't have a clue about the differences between single family and multi-unit investing and these idiots are telling their clients that single family properties is where the big money is. I seriously feel like punching some real estate brokers for being either idiots or liars.
Never mane an investment decision unless you are 100% positive that it is the perfect deal. Never guess. Never make a decision based on advice given by a broker, investment advisor, attorney, your priest, friend, another investor or family members. If you need to rely on advice from any of those people you are not ready to invest one penny.
Research hundreds or thousands of properties and don't waste your time looking at a property until after you did the math. Otherwise, you waste a lot of time going on wild goose chases. While your investment decisions may change for the better after looking at a property there is a certain amount of wild guesses you can figure out by knowing the neighborhood and seeing a street view picture.
Never buy properties solely to purchase, rent and pay down the mortgage because you will never get rich collecting rents. The big money is when your property value appreciates, or when you can do some improvements e.g. adding a bedroom and bath and increase the value of the property, but this requires many skills that even pros have because they lose money all the time.
For a beginner, the biggest profits are with multi-units even as small as a duplex, but as the number of your units increases your profits are exponential.
Well, I need a million pages to finish and have to go back to my regular job.
It is hard to lose money if you don't do anything. You can lose your entire life savings when making one bad decision. Money is hard to earn and super simple to lose. I say this because there are too many people who have real estate fever so bad and they are so blind they think they can't lose money when investing is real estate.