"Best" depends on what your goals are and where your starting from.
Many good sources are available at your local book store at very reasonable prices. Avoid the late night infomercial guys... most are no more useful than a $20.00 book you can pick up on the same subject.
Key thing I have noted, is that many are simply a re-package of already known material but often with a few new ideas tossed in that you have to find.. so read different people's inputs and be rounded and don't start thinking that any one guru is the single source of real knowledge... that would result in your personal and professional failure.
Are your interest in re-habs?, long term residential rentals? long term multi-family units? apartment buildings? land development? short/ long term asset appreciation? income streams? fast cash?
Develop a business plan... easiest way it to do one is backwards... start where you want to end up and work backward to how to get to that point. When you have a plan, then you can start executing and measuring yourself against it. Adjustment will always have to be made, so review the plan often and keep it current. From your reading and that plan will dictate what type real estate investments you need to concentrate on and when in your development. If you get to the point where you need to ask questions... ask someone (several) you know have been where you are. They can advise you on what worked for them and what didn't... it may not be the same for you and your area but you may find it very informative in specific circumstances.