CS can always be improved until you're the best, but honestly this game stresses conceptual knowledge far more than mechanical skill. Your decision making at all stages of the game is the most important factor, you can reach plat with average mechanics.
I've known a couple of friends in Bronze to rant to me after every loss about how bad their team was, and that they're better than the League they're in and should be higher. If you're that superior in skill to the people you get matched with, you will constantly crush your lane and use your gold advantage plus your tactical understanding to get your team to make smart plays and win. The #5 ranked player on the NA server recently did a one week stream where he went from Bronze to Diamond I. His record to get from Bronze to Plat was something like 55-4 (He played jungle).
Obviously none of us are as good as he is, so I don't expect you to carry games like that, I just want to point out that if you have the skill of a higher Elo player, you will reach that Elo. I'm not saying that you're condemned to Bronze for life, almost everyone has the capacity for improvement, I've watched my friends who spent a long time in the same rut commit themselves and go from Gold->Diamond in one month.
I think that for most people watching an informative stream is one of the best ways to improve. If you have the critical thinking necessary you can do it yourself, but you'd probably have to record and then analyze your games because it's difficult to do that in the heat of battle. Most pro streams I wouldn't recommend watching, it's usually someone who offers no to very little commentary, with a few exceptions. Nightblue3 (the guy I mentioned earlier) is probably the best one you can watch, he will explain everything.
I looked at your champions picks and here's arguably the strongest champs for each role:
Top:
- Mundo - The new defensive masteries have made him very strong. His early game is weak until your cleaver is ranked up a bit, then he can dish out some damage.
- Shyvana - She received some buffs a while ago and has seen a return. She does a ton of both physical and magic damage and is difficult to kill.
- Riven - Always been a strong champ, either she was just nerfed last patch or has a nerf on the PBE, but she will still be very strong. She's actually more popular mid now since the squishies there are easy targets for her.
- Rengar - If you win your lane you will be able to instantly kill any of their squishies. If you lose lane, build tanky, still has good damage on with spirit visage + your W you're very difficult to kill.
- Renekton - He's been popular for a while now, since he started getting picked last year in the LCS; still good.
- Jax - Saw a comeback with the buffs to Tri force, you can build him tanky, do a regular build, or go AP.
Mid:
- Ziggs - Probably the strongest mid laner there is right now. Strong in lane with great team fight presence. Sieges well and has good poke.
- Syndra - Nukes squishies with great efficiency, probably has even more burst power than Leblanc.
- Yasuo - Strong but his win rate indicates people have great trouble playing him. He has almost assassin-like damage with amazing utility and decent mobility and survivability. You might want to avoid him unless you can master him, not easy to play.
- Kha'Zix - Great carry potential, his damage on an isolated Q is obscene.
- I haven't seen a Diana since her last nerfs, back when Dig was crushing everyone with her; I don't think she's a top pick anymore. Lux is just alright. Kassadin is very good.
Jungle:
- Kha'Zix - Same reasons he is good mid, he gets great clear times once you get some levels, has strong ganks and snowballs hard. Evolve your Q first.
- Vi - Good clear times, very strong ganks, she's a threat at all stages of the game.
- Elise - Tanky champions are really popular, and Elise's % damage is great against them. Once again, good clear times and ganks. I would build tank Elise with a little mpen.
- Udyr is strong, but just not quite as much as these other champs.
ADC
- Jinx - Does a ton of damage with good range.
- Draven - He's strong in lane and snowballs very hard.
- Sivir - She was buffed a couple patches ago and has been very strong ever since.
- Lucian - His passive is very strong and he has a good dash.
- Twitch isn't as strong as he used to be, Kog is just kind of average, but if your record with him is really bad something isn't right. Kog is pretty weak early because his base range and damage are low and he needs ranks on his W, he lacks the burst that other champs can put out. Play safe for the most part and farm. Once you have some ranks on your W you can harass almost with impunity.
Support:
- Thresh - He's always going to be a top support because of the insane utility his kit offers.
- Annie - She's stronger than most ADCs early on, has a reliable stun, AoE stun, and massive burst.
- Leona - Tanky initiator, excellent CC.
- Taric and Soraka are a little weaker right now. Soraka should get instagibbed early by the Jinx/Draven + Annie/Thresh hyper aggressive lanes that are popular right now.