PKRING'S GUIDE TO CARRYING (applies to most champs, ignore 1. if supporting and 2. if jungling)
0. DON'T DIE. Easier said than done, but don't overextend, watch the minimap, position well in teamfights. If you're feeding, then you're NOT carrying. Ward when needed, but don't waste gold if that ward isn't going to give you vision of anything important.
1. FARM. It's safer/easier to farm minions than champs, so until you consistently have at least 100ish cs before 15min EVERY game this should be your main concern. Take wraiths if they're up and your lane is pushed, either yours or theirs (but watch the minimap while doing it)
2. WIN LANE. When all the enemy minions are full health, don't just run around doing nothing. Poke, zone, harass, even autos are wonderful harass in every lane. Get them low so that once you push hard, they have to go back. Killing them helps win lane, but don't take massive risks unless you can see their jungler on the minimap.
3. WIN OTHER PEOPLE'S LANES. If their mid went back and you're winning lane, grab wraiths and gank their bot, top or jungle. I generally prefer going for bot because double kills are better than single kills, but whatever's not warded works best.
4. TEAMWORK. Ping objectives as soon as, or even before they're up. Get your team together and steamroll the enemies. This can be the trickiest part because often, people just won't cooperate. Just take those who do and do your best. Not every game is winnable, but many games are.
5. TEAMFIGHTS. If you're fed, make sure you're doing damage without getting focused, so you can continue to do damage. Landing skillshots, initiating etc. is all important, but really you just need experience to make fast, good decisions.