Beat me to making this thread. :(
Anyways, Defense of the Ancients differs from League of Legends.
The most unique mechanic in DotA is creeps and farming in general. Blocking creeps, pulling creeps into jungle camps, and denying your own creeps just so you can end up having more money than your opponent in lane. Keeping creep equilibrium is important (in lower ranking mmr this doesn't really apply, it's just good to practice).
Another unique feature to DotA is the fact that you can control more than one unit. There are many heroes in the game that can take over creeps and use them to their advantage, all while controlling your own hero at the same time. Meepo is the hero that I play religiously, and you have four other meepo clones to control. Some of the jungle creeps can give auras to help out. Some examples of these auras would be attack speed boost, damage boost, defense boost, healing boost, etc.
The best thing about this game is that all the heroes are unlocked. You can play anyone you want, and you don't have to save up points or buy points to unlock them earlier. Only thing that Valve puts out for sale is hats and HUD skins. You don't need these at all, they just make your hero look cooler. (y)
DotA is just more complicated to play, but still easy to learn. If you already have League mechanics down, then DotA should be no problem for you in low mmr.
If I have any more to add, I'll do so.
Glhf, friends.
Edited to satisfy Chrono.