upgrade your ward at lvl 9, or at least before lvl 11. you can reach the 3 ward cap just through upgraded yellow trinket
learn to play from behind and call shots. when you're losing telling your team to stay in base, don't chase, and don't leave turret range is amazing, because eventually the enemy will get impatient and try to fight what may as well be a 6v5.
mute anyone being negative and don't insult or rage at anyone. if what you want to say isn't a strategy, advice (not negative criticism), or a joke (not at your teammate's expense, this is to raise moral) don't say it at all.
remind your team that raging at eachother achieves nothing. so panth tried to 1v3. calling him a moron isn't helping. reminding him not to try to 1v3 is helping. normally someone else will see you trying to stop the argument and jump in to help you.
NEVER SURRENDER. i had a game where we were losing in every way possible, especially bot lane. then our adc got zoned out of a teamfight by their adc and supp, and while we won the 4v3, he somehow got a double kill and started to carry hard. there's no real explanation for how we turned it, we just did. so een when you have no idea how you could possibly win, press no anyway. those low elo throws are real 0_o
stick to just 1 or two main roles, and one or two main champions for every role. i main udyr/panth jung and brand mid. for top i have garen/udyr, adc is ashe/jinx, and supp is brand/taric. because i only play like 6 champs, i know those champs better than most people at my elo will know their champs, so i can win matchups i'm not even supposed to win. sivhd can get a pentakill with katarina playing with one hand; he seriously sits there on stream with his webcam on screen and an apple in his hand deleting people left and right (can we turn this into a 'nerf kat' thread instead?). he also one shots enemies with ap ezreal.
play when kids won't be online. as a college student, i have the luxury of playing late at night or in the middle of the day, so i can tell you there's a difference between playing at 10am and 10pm. i went on ranked hiatus for two weeks after two of the most toxic games i've played all season made me realize the kids were on spring break.
Don't play after a hard loss. i have a friend who will drop like 3 divisions in a week because he thinks he doesn't go on tilt.
kills mean nothing after laning phase. if you can get a kill or a turret, go for the turret. i see so many people get an ace then recall, and i just spam the pings like WTF THE TURRET IS RIGHT THERE! the kill may turn in to a death or two anyway because these people refuse to ward. also learn to leave your teammates behind, because a single death is better than a double kill.
watch some gameplay from pros, especially people who explain what they're doing and why they do it.
honestly, unless your time is limited, you should play a lot more normals than ranked. normals is how you learn to do the things you need to apply in ranked.
there's probably a lot more, but seriously, it's really just about experience. if you have a lot of time and no skill, you'll eventually be better than someone with a lot of skill and no time. you look on youtube and see people like keyori just derping around playing every champ a-z and dominating with 90% of them; and it's not because keyori is godlike, it's because uberdanger carries him he plays every day.