My advice: follow the flavor of the month, or a seasoned veteran that's infamous for being good, and is still used all the time. I found a champ I'm good with, but is sorely outclassed in this meta and gets wrecked by AD assassins which are popular because they're so flashy and are played often in the LCS. Don't pick someone complicated like Zed or Yasuo; go with champions like Annie that are just so standard because they're simple, and they work.
Personally, I find it especially hard to climb when supporting with a poke support; your mileage may vary with engage supports like Leona or Blitz, but with, say, Lulu or Janna, you will probably have issues. Support in general is kind of hard to carry with; you have to be extremely good, and have a lot of faith in your carry. If they don't follow up, your as much as screwed; I'd leave this role if you could, but others will say it's a sure-fire way to climb. I dunno.
As Tsoul mentioned, don't play if you're angry. From experience, I'd say leave it after one loss, but, again your results may vary. I was able to lie to myself and say I wasn't tilting last season, and it got me dropped into bronze 5. Trust me, you don't want to be there because your team is a crapshoot every time. You will go on tilt so often because some of your team mates will be so horrible there is no working with them. People that just straight up shouldn't be playing this game show up here. There are so many, I'm still stuck there after being almost silver, and going on tilt.
Don't get TOO experimental with your builds, but remember that there is something you can do to push objectives on most champions. If you have a lot of AP, consider a sheen item to take towers if your team just can't. Lich bane with 600-800 AP deals some pretty reasonable damage to towers, to justify dropping the gold on it. If you have a lot of HP, maybe consider titanic hydra. If you're adc and you're having trouble taking objectives... focus objectives, man, what are you doing? Most adc's are really good at taking towers because they usually build high attack speed and high attack damage. If you're support and don't have much of any of those things... well you're a little screwed, but just do your best.
Also, jungling is a bad idea unless you have a real talent for it; you will get flamed the most out of any role and you will be expected to do way too much, and there's too much pressure... unless you can do it well.
Another thing about champion selection: Don't pick something you don't really like just because it's "OP". Kat is "OP" but I'm bad with melee-range champions in general with a few exceptions. I just can't play Kat that well, and don't do well with them, so I don't play her.
Oh, and don't play Veigar. I'm good with Veigar, but he just gets fucked by a lot of mids, so either you'll get bulled out of lane or killed a lot as Veigar, I'll tell you from personal experience. All of the champions that you have a great advantage against are mostly out of meta picks now that people want to make the plays with AD assassins like people in the LCS... so, you know.
Tsoul also did a great job mentioning that you should know what most champions can do so you're not taken by surprise when you realize that, say, Talon gets borderline unfair damage buffs on slowed targets because of his passive and he has a Shunpo-style blink...
I'm totally not salty about anything. Nope.
But seriously, fuck Talon.