How do you win in a newbie game?
Firstly, play someone tanky but powerful. You'll need it.
Secondly, either get a lot of kills, or proceed to be the best in saving your teammates as possible. The second only works if you are tied fairly well with the enemies.
Thirdly, become the master. Lead your troops into battle. Give them a nice plan for what to do, and by God, tell them exactly what they need to do. Got an Alistar that smashes away the enemy carry? Tell him to use that on someone else. Specify someone. Got a suicidal Graves that likes to be a hero? Tell him that you are now the hero, and that if you die, you are not important. He is the important one. You are there to save his life. Got a roaming Olaf that doesn't listen to you? Make everyone else go mid so that his roaming is actually incredibly useful as a distraction.
Fourthly, make everyone feel important. Do not tell them they suck, because even if they do suck,, they no longer like you. See a good play? Give them a pat on the back. See someone die? Tell them to stick with you, because you won't unless you have to.
Fifthly, go down with the ship and give them the lifeboats. I don't care how important you are, it is better to lose only yourself than it is to lose 4 of them. The enemy is one-minded. They will hunt you down if they can. So, let them. Even if you're full health, they will give up on the weaker prey to kill you. They know you're a threat. This gives your team a chance to live. If you lose all 4 of them, you lose. If they lose you, then you are able to talk to them. That is at least a little more useful.
Sixthly, if you don't have anyone else to go in first, do it yourself. This is the problem with newbies. They are afraid to go in first and die. Show 'em how it's done.