There is a vast amount of knowledge out there on computers! In fact, it is so vast that no single person could ever possibly ever learn everything there is to learn about hacking or computers in general. People usually specialize in a certain field: cryptography, computer security, networking, software development, testing, and so on...It's probably a bit premature to decide what you want your speciality to be, but keeping the question in the back of your mind will help give you direction in the future.
Hacking is all about understanding what is going on inside the computer and then figuring out a way to modify it to better fit your needs. Not all "hackers" are maliciously seeking out security holes to breach multi-billion dollar corporations in order to gain money or sensitive information. In fact, most hackers I know are just people who love learning about computers! They love manipulating computers so that they can accomplish tasks more efficiently. Remember that knowledge is power and power can be used for good or for evil. What is good or evil is a rather relative question and that's up for you to decide? Without getting too technologically philosophical, let's move onto ways in which you can gain knowledge in a fun and effective way.
Well, you have made the first step by finding a blog such as this and showing an interest to learn about computers! A blog is great because you are continually receiving little bits of information. It's not the quickest way, but a great to keep up on new hacking tactics and refresh your memory on general computing techniques.
If you want to progress more quickly, then the first logical step would probably be to learn how to program. Programming skills are probably the most valuable skills to have! The best way to do this is by trying out your own little projects. This could really be anything! You could create your own website, try designing a simple game or create an application for your phone, etc...Basically anything that sounds vaguely fun to you?
Don't really know how to program? There are a ton of online resources at your disposal! If you don't know how to do something, simply "Google" it and chances are someone has already had a similar question. A great comprehensive website is W3Schools. They have an outline of most of the basic programming languages you will need to understand how websites and programs on the internet work.
Another great site is Hack This Site, which allows you to test your hacking skills literally by hacking a real website. You will learn about everything from SQL Injection to XSS attacks, it's a rather entertaining site if I don't say so myself!?
More recently, Stanford has begun development of free online classes regarding everything from cryptography and CS-101 to Game Theory. It is supposed to launch within the next month, click here to check it out.
Besides the internet, don't forget the library! Your library probably has dozens of books on programming, networking and computer security. Go pick some up and peruse them just to see what interests you?