Newb needs help

I've been playing DOTA for a little over a year now. I haven't played too much over the year. I played a lot a year ago, and I play a lot now. In between I got into Starcraft, but I really want to improve at DOTA. I feel that I could be good but I don't really know where to start improving. I honestly don't even have a role that I play. When I play with my friends I carry, but that's only because they have been playing for about a month (I got them into it). I'm almost level 13 so I can start ranked matches soon. I have heard that at my skill level ranked matches isn't the best idea. So basically I want to get better and I don't know how. General advice is greatly appreciated. Really any knowledge you have to offer me would be great. Thanks in advance.

It's true that you don't want to play ranked right off the bat. I dug myself into a .5k MMR Hole and have not played ranked since, so I am still about 1k MMR.

As for general noob advice,

Create a hero pool

Choose 8 - 10 heroes that you can play well in almost every situation. This should include 2 supports (ex. Sand King), 2 carries (ex. Luna), 2 tanks (ex. Axe), 2 pushers (ex. Nature's Prophet), and 2 heroes of varying roles ( Maybe nukers like Zues or a ganker like Night Stalker). This would give you a few heroes to get good with, and to give you some default heroes to play for if you just aren't quite sure what to do.

Awareness

Dota is one of those games where you must be paying attention o EVERYTHiNG all at once. Know where people are, how much health they have, what spells they just used, and how much time until they can use it again. Know what kind of strengths and weaknesses enemies and allies have. Know when the right time to use your spells are in conjuction with your allies. Be aware of how much mana you have and how much each spell combo costs so you don't waste to much mana. Make sure that you are pulling creep waves, stacking camps, watching the day / night cycle, watching to clock so you know when the runes with spawn, refill your bottle with runes, keep track of what items your allies are building and how that can affect you and enemies. Be aware of EVERYTHING ALWAYS. You CANNOT afford to be selfish in Dota 2 or you WILL fail.

General Tips and Tricks

• Keep a TP on you at all times
• If you know you can get a rune, use your Bottle before grabbing it, it refills the bottle charges
• Spend your starting gold wisely, never buy any item over 250 gold when you start unless you know what you're doing.
• Deny ( Default button is 'A') as well as last hit, you don;t want your enemy to get gold.
• Stay on the high ground when possible ( More Vision, Ranged Heroes below you will miss some attacks )
• Teamfights are priority. Doesn't matter what you are doing, always TP into team fights if the situation is reasonable ( If its 1:2 don't go in )
• Make use of your Alt clicks as much as possible. They can tell your allies cool downs, your HP and Mana, your lack of mana, the time, and can translate quick messages with hotkeys (if you set them)
• Don't risk. Odds are if you are risking it, you are losing it. Don't. Only pros can risk.
• ABOVE ALL WORK WITH YOUR TEAM. THOSE WHO WORK TOGETHER WIN. I know, it's hard in pubs.

Your greatest advantage right now is you have friends you can play with, they will listen and cooperate. Without cooperation, you cannot win. The funnest matches are those where you team works together well and works together to do a task, whether it be pushing or killing or defending.

Your calibrated MMR, when you eventually play Ranked, will take a lot of input from the level you're playing your Normal matches at. So if you want to dive straight into Ranked calibration from a new player's perspective, you are likely to calibrate low.

That's not to say that isn't a good thing. It means that when you improve, you will raise your MMR quickly. It's just many people are at low MMR for a reason, and it's generally because they aren't improving. So bear that in mind; the skill level of players won't be very good for the most part.

Personally I'd get some more experience before you dive into Ranked, so you can at least calibrate at the 3k MMR level. Alternatively, if you can get to the 'Very High Skill' level of matchmaking on your Normal games, this usually signifies that you'll be calibrated at 4k MMR or so, provided your calibration doesn't go too drastically.