Learning Magic the Gathering
[Warning: gratuitous babbling ahead...]
I suppose most people learn Magic the Gathering from a friend, from the rulebook that comes with the cards, or from online sources. Of course, I had to be different. :-) Back in ~1996 I had no internet connection, and didn't know anyone who played the game. 1 What I did have was a couple of old Inquest magazines that talked about it, and it seemed very interesting. Then, at some point Microprose Magic was released, and I went out and bought it (even though technically I could not afford it, and technically did not have a computer with the specs to run it ;-). The rest, as they say, is history.
So, I learned the rules from a computer game. Typical. Unlike most people (except those who have been there since 1993), the first cards I got to play with were from Alpha/Beta/Unlimited (including the Power Nine), and Arabian Nights.
This allowed for interesting possibilities, of course. Channel/Fireball deck? No problem. Deck with multiple Black Lotuses, Moxen and Black Vise? Perfectly OK.
This post is not just about that, however. It's possible to learn the rules from a book or tutorial, and you gain strategic insight by playing. But what the game could not do, of course, was explain why certain things are the way they are. There are many things that aren't immediately obvious until someone explains them to you.
By the time I got an internet connection, I went on the Magic newsgroups with a lot of playing experience, in a way, yet at the same time being a "scrub". Suddenly I learned a lot of new things, the hard way.
For example, why are Moxen considered good? From a beginner's perspective, they do the same thing as lands, so why not just play lands instead? The answer is, of course, that you can only play one land each turn, and a Mox, being an artifact, allows you to play an extra mana source (in addition to a land). More mana faster = advantage.
For the same reason, Llanowar Elves were popular; you can tap them for an extra 
, which means more mana for you than you normally would have had from just playing basic lands.
Will-o'-the-Wisp was another example of a card that seemed useless at first but was actually really good. Being a 0/1, it seemed unimpressive to say the least. What I didn't realize until it was pointed out to me, is that it makes an excellent blocker. For 
, you get a card that blocks pretty much anything, including fliers; and if you have another black mana to spare, it regenerates and can do the same trick next turn. With Bad Moon and/or Unholy Strength, it suddenly becomes useful for attacking as well (and Dark Ritual was still around then to pay for it all, so things could get out of hand quickly).
Anyway, what the rulebook doesn't tell you, but what you can learn from other players, is this: you shouldn't look at cards in isolation, but rather, look at how they relate to other cards. I don't just mean combos (like the infamous Channel/Fireball mentioned earlier), but rather a more holistic viewpoint. For example, black doesn't have the best creatures. As a beginner you might notice this when comparing the kinds of creatures that each color gets. Instead of assuming that creature X sucks, or that black sucks, you should ask what black does have that compensates for this.
A useful (and fun) exercise is to find a card that seems sucky (and there's lots of them), and find cards that make it not suck. Let's say that a creature has islandwalk. Great, but what if your opponent doesn't have any Islands? Then you should find cards that make sure they do have an Island. Card X makes you discard your own cards? There are cards that just beg to be discarded and turn it into an advantage; find them and add them to your deck! And so on.
I think learning these things nowadays is much easier though, with so many sources available online, including dailymtg.com, which explains rule changes, design decisions, and much more.
~
1 This was in the Netherlands; back then you were less likely to find players there than in the US, where the game originated.