I think the key to learning DotA, or melee in general, is the same way you learn how in many cases: Research. If you research before hand what works, and what doesn't. You can cut the learning curve drastically. That is how I managed to get far in Diablo II Zy-el, and any games in general. Hell, if you /profile Okamizu_sama@Azeroth, you will find I played almost 4000 games of Melee. I can be very helpful if you wish to learn Melee, and so can Theroy.
If you want to learn how to play, first find out about what heroes interest you. Are you into rangers, melee guys. Then look at the Allstar database, and check out the spells for the heroes. Then actually play the game, via trial and error and see how you do. If you think you are getting the hang of the hero, continue practicing as him or her to get the basics down. If you are having problems, try something else.
As you get better, then start finding out which item/skill builds are right for your cause. And learn to deny creeps by killing them when they are low on Life. And to pick off weakling enemy creeps so you can get the kill, and score Gold faster.
I recommend doing allpick games until you get the hang of what is good, and what isn't. Allrandom is mostly for people that can adapt fast, or are generalists when it comes to DotA.
And if there is an opportunity, and you have checked for any dangers, then take it and hope for the best. Because it is a common strategy to take advantage of others who least expect it, or are unprepared.
I personally learned the game this way, using mainly Strength, melee heroes as my forte.
It was when I played as Lycan that I started getting the hang of things. And don't forget to read the spells carefully to make sure you know how they work. That way, you don't blow an ultimate on something that is unnecessary. And you dont stack orb bonuses on top of each other.
. Never did get what's so addicting about them anyways.
