One thing I'll suggest is to look up some general guides for dota and practice things that are useful for any hero. Things like how to stack creep camps, creep blocking, properly pulling a lane, good ward spots, juking, etc. I could show you this stuff in game but it'd honestly be just as easy to watch someone else do it. Maybe watch a stream. I recommend this guy:
http://www.twitch.tv/barnyyy Watch some of his videos and listen to him when he's telling people how they're fucking up. He's usually right and explains things well. He also uses a lot of the tricks I mentioned himself when his allies are too dumb to do it on the heroes that should. He's not an amazing player or anything, but he's a better than me and a lot better than your average player. He also makes it pretty clear when he's trolling or being sarcastic, and generally assumes his viewers don't know fuck all. Be careful who you end up listening to though, streamers especially say all sorts of bullshit and never admit they're wrong because it'd make people leave the stream. There's a guy called Purge that uploads on youtube, and he's fucking awful, but people follow his advice all the time because he says he's good and he's the only guy on youtube really. He also casts games, which is another thing to avoid. Most casters are awful and are only their to yell excitedly when people get kills. Anything they say about the mechanics is usually wrong. Another thing people often do is try to copy something they saw in a high level game without understanding why it was done. Huge mistake. Most of that stuff isn't even applicable unless you're in a steady team that is all very good.
Other stuff to learn is things like hero matchups and individual ability uses and combos, but that's a lot of shit to learn. Try taking a look at
http://stats.dota2.be/herostats when deciding what heroes you want to play. If it seems like a simple hero and has a low win rate, chances are it's an awful hero. Good heroes either have high win rates or are very difficult to play (and have a lower win rate because noobs always fuck them up). One last thing I'll say is regarding items: Urn of Shadows, Blink Dagger, Scythe of Vise, Arcane Boots and Mekansm are all excellent items, even on the wrong heroes, because they help the whole team out a lot (well not blink dagger, but that is just amazing.) Dagon, Phase Boots, Aghanim's Sceptre, Bloodstone and Shadowblade are all hugely overrated items that are each only good on two or three heroes in the game. Maybe a bit more for the sceptre, but it's awful on a lot of the heroes it still has an effect for. If the game recommends any of those items in the shop, it's probably still a bad idea. Oh, and always, always always carry a tp scroll. Preferably 2 so you'll still have one after using one without having to run off and buy another. It'll make you money in the long run by escaping from people and getting to pushed towers before all the creeps die. And tping in to save an ally makes you look like a fucking genius.
