1°) Pick a carry.
Now you may ask yourself, what is a carry? Well, a carry can be any hero really, what really defines the role is the lane you chose. If you chose the safelane, you are a carry. If you chose the midlane, you also are a carry. If you chose the jungle, you clearly are going to carry in the end (not the first 20 minutes though, obviously). And, depending on the game, offlane can also lead to hard carrying your team.
On rare occasions, even a fucking solo support can become a carry, but it implies a bit of dirty work to get there. So that's not the best choice.
2°) Get farm.
So that's basically where shit ain't in your control anymore. If your team is good and your support is not a fucking retard, you will be able to dominate your lane and probably get all the last hits (minus the impossible ones, minus the time you run back to fountain because your support sucks, minus the time you die to uncalled "no ss ?" ganks, of course).
If for whatever reason your support accidentally takes one last hit, or, god forbid, steal the kill on your enemy, make sure to stop everything and type inflammatory comments in the ally chat. It's pivotal to your success so you can forego a lot of farming time, tank creeps, even die while typing this : you need to assert dominance in your team as well. YOU need the farm. All the farm.
3°) Get more farm.
Killing creeps is very important but you also want to kill enemy heroes for obvious gold swing reasons. So don't be a pussy like your teammates and just fucking kill enemy heroes.
Now if you play with a bad team comprised mostly of shitty teammates, this may lead to unwanted situations where you are left alone under their tier3 tower at minute 5. How are you supposed to carry the game, when nobody helps. I have no idea either.
What you can and should do though, again, is let your team know how bad they are playing right now. Why are they not helping? Why is there no wards at the exact spot you died? Why doesn't your mid ever call any misses, or only do so when you're busy last hitting and obviously can't see shit? Also not ganking at minute 5? Maybe they simply want to fucking lose, or maybe your mid is a retard. Could be both.
At this stage is it okay to engage in a somewhat in-depth discussion with your team mates, to pinpoint where the problem is coming from. In doubt, here are some efficient keywords : "reproted", "let them end", "all mute gl" and of course, the crowd favorite "fucking wards".
4°) Ask for wards.
Wards are the most important thing in this game because it's basically a legit maphack and your fucking noob support should know that and place wards everywhere you will go in the future.
Wards have a second effect though, well known of every player in the 3k bracket : they will excuse and explain any death.
Whenever you die or get ganked, all you need to do, is press your chat wheel macro : "We need wards". Now everyone including yourself will know that the fucking support is to blame for this loss. Yes, that clueless fuck who initially wanted to be mid, then jungle, and finally had to last pick the only support and still can't play it, I mean why even pick a fucking support if he can't play support, does he want to be reported? How are you supposed to carry the game, when nobody can fucking ward. I have no idea either.
Now, from times to times, some smartass will point out that there is no more wards to buy in the shop, or that there were already wards at your location, or whatever bs they can come up with. Don't let that distract you, it simply means that they are not using them well. From here, you have 2 options, say : "kk afk farm" OR say "deward".
Saying "deward" is a very strong move, because you can't run out of them. So as long as your support has 100 gold, he should be dewarding without stealing YOUR courrier. And he will get 100 gold, meaning that in the end, he's the one not doing his job. How are you supposed to fucking carry the game when no one is doing their jobs, no idea I'm telling you, but that's also why this guide is for 3k, not 4, 5 or 6k.
5°) Carry the fucking game.
Carrying the game basically mean getting more farm and killing enemy heroes. Don't bother too much about "objectives", it's mostly a caster term and your hero should be very strong at killing creeps and chasing enemy heroes, so this it what you should do.
So just do that and carry. Go to a lane, kill the creeps, get jumped by 3 fucking heroes because no wards, almost kill their support with your ultimate, die to their carry because you get no help, flame your fucking team for no wards/deward/help, type "gg" in all chat, wait your death timer, and repeat.
That's your midgame right there.
Now, because you are playing with 3 other carry and one wannabe carry (aka solo support), you should all be doing the same. Namely going alone, trying to get as much farm as possible, chasing heroes until someone dies (with zero fucking help, still), and dying to ganks.
All in all, the midgame sucks for a carry, but that's not your fault, that's just how it is, when you play with dogshit teammates that have no idea how to play the game of dota2.
6°) Wait for the enemy team to make a mistake and get 4k gold.
At some point the enemy team that should more or less play like your team will massively overextend under your T4/pool while pushing. Just wait for that very moment, hide a little bit during the push, or pretend to be AFK (or keep farming, you are a carry after all), but try to be there for when they dive your fountain.
This could result in a 4k gold in your favour.
If for whatever reason this does not happen and they play like pussy or just die before you TP back, or maybe you couldn't even get the fucking TP scroll because everyone keeps stealing your courier, or you know, Slark killed it when you called it, or any other event resulting from the fact that your team does indeed suck balls and you'll never get out of this bracket, then the game is probably lost.
7°) Late game carrying.
So here comes the late game, each team has given up multiple times already but everyone is still playing. So now what should happen is that your team should play around you, seeing that you are the carry, and just follow you around as a unit.
However, since your team is comprised of basically 5 carry, well, you get 5 people all expecting the 4 others to follow and protect them. Which, unsurprisingly enough, translates into everyone still wandering alone, trying to make big plays on their own versus the 5 enemies, failing, and dying for a oh-so-very-long-time, seeing at this is now late game. Probably with no buyback either.
Or maybe it is you that died alone without buyback, but again I mean the map is dark, nobody was stopping their push, nobody ever bought dust and nobody ever helped you basically. And you need items, you are the fucking carry. So yeah, gg. How are you supposed to carry these clowns, no idea mate.
8°) Win anyway.
Because you are a strong carry. So when their team ends up killing themselves in your pool with no buyback, and that stupid-useless-from-the-start LC jungler and your noob no-skill-zero-gank mid both manage to somehow finish all their racks thanks to all the lane pushing you've been doing, well you may still win the game.
So yeah, you still managed to carry those noobs. That's just how strong you really are, I mean, I knew you were good but... that's still impressive.
Out of respect for yourself and the enemy team, you can and should type "ez [insert their carry name]" and "comadn".
Another good game of dota2, you're improving by the hour (this guide probably helped, let's be honest).