You're main issue just from reading, is that you're maining support. In low elo, that is NOT an option. If you have decent mechanics, and can last hit and know how to kite and position properly in lane and in team fights, there's no reason you shouldn't be playing an ADC or going mid.
The best way to climb, is to practice carry rolls and have an off carry roll prepared for when you don't get the two you want (IE learning mid and ADC main, with jungle on the side) And climb that way.
As someone who ran a diamond team, I can give you a bit of help.
Mid: Lux, Varus, Ziggs.
Lux: Pro's:
- E is long range/safe poke with high damage.
- W is team wide AoE refreshing/stacking shield.
- Q is a two person snare with semi-okay damage.
- R High burst damage AoE ult that late game can 1 shot someone like twitch or Sona.
- Passive Dealing damage from your Q, E or R allows you to proc a scaling with level/AP mark with an Auto for extra harass in lane.
- Very small learning curve
- Easy to pick up
- Very long range
- Great team fight ability
- Great wave clear
- Can also be played support
- Can use ult to gank from half a lane away
- okay early game, great mid game, Great late game.
Con's:
- 100% skill shot reliant
- No dash/blink in a mobile meta
- Semi costly in item build
- W ratio is pretty low until you get some hefty AP (or if you're support, just max it)
- Need either
or 
(which was nerfed recently) in order to be somewhat "tanky"
- Assassins take her out for dinner, but forget to inform her that shes the dinner.
- 3 E's early game if you don't last hit well with Dorans ring WILL OOM you.
Summoners:
Support: 
Mid: 
OR 
OR 
OR
Never take ignite, because you should almost never be in range of the person you're facing to use that summoner.
Build (no specific order just in general):
OR OR 
Varus: Pro's:
- Q is very long range high damage harass that's AoE
- W gives you %HP damage when you auto attack champions/minions and consumes that %HP per stack (up to 3 stacks. great for shredding tanks!) When you use your Q or E on the enemy champions/minions.
- E AoE slow
- R Single target that spreads into an AoE over time that applies 3 full stacks of your W to every champion caught, & roots them
- Passive allows you to last hit faster/easier as you gain attack speed per minion/champion kill (Less for minions)
- Very long range
- Fantastic Harass
- %HP damage is useful against EVERYTHING
- Builds Lethality/Amr pen for free damage on tanks (late game you can half HP an APC or ADC with just one Q)
- Kiting is great with your E/R
- High base damages
- R allows you to stay safer in the shorter lane (mid) as you can stop the jungler/mid laner (Most times both at the same time) with just your R
- You out range almost every champion with your Q
- Heavy poke
- Great early/mid/late game
- Low learning curve
Con's:
- Very low base movement speed
- Requires CDR to be effective
- No blinks/Dashes
- 100% Skill shot reliant
- Need 2ish items to be relevant
- Costly item build
- Q slows his movement speed even more
- Q is a charge ability
- Doesn't get tankier items like mages ( IE no ROA)
- Mobile mages/Assassins if they get to you, you're most likely dead.
Summoners:
OR
Should never be in range to use ignite, and Exhaust isn't worth running because if you have to turn around to use it, chances are you're dead.
Build (Personal Preference): 
Ziggs Pro's:
- Q is long range harass
- W is a tower nuker and a escape/disengage tool
- E is an AoE slow
- R is an AoE nuke
- Passive is free damage every 10 seconds every auto attack based on your level and up to 50% of your AP
- AoE heavy
- Great team fight
- Self disengage
- Poke heavy
- Wave clear
- Tower pushing ( add lichbane for lulz)
- Can kite well
- Glass cannon nuker (personal preferance for pro! xD )
Con's:
- 100% skill shot reliant
- Squishy without ROA and similar items
- Q can bounce and miss targets
- W can either save you, or place you into something you didn't want if you miss time/miss click
- Can be pushed out by champions like Varus/Lux
- Assassins brought Ziggs to the same dinner party as Lux
- Glass cannon
- Mana items are a MUST or you'll go OOM in 2-3 spell rotations (EVEN LATE GAME)
Summoners:
Build: (Fast tower pushing/ instant wave clear with high damage)
ADC: Cait, Jinx.
Cait pro's:
- Q high base damage/wave clear
- W snares, can place up too 5 at a time (max rank) to use in choke points or around turrets to stop sieges
- E slows the 1st enemy hit and knocks cait back also procing her Headshot passive if you're in Auto range
- R long range single target, point and click nuke
- Passive gives you a heavy damaging auto attack every 7 shots (2 shots if you're in the bush)
- Somewhat mobile with E
- wave clear
- 1v1 potential with just 2 items (usually IE and Hurricane or Static shiv)
- Good kite
- Heavy team fight damage
- low learning curve
- Lane bully with Q harass/wave clear
- Passive procs on turrets
Con's:
- Somewhat low mobility
- R can be blocked by enemy champions (Also item effects like Hourglass can put it on CD if the bullet animation is cast)
- W isn't very useful if you don't know how to set them up effectively
- E isn't useful in lane
- Passive requires auto attacks prior to use
- needs long range mage supports or super tanky melee supports (Zyra/Naut)
- Falls off a bit late game
- Early game can be rough if your enemy support/ADC is able to out push/harass you or your support
Summoners: ( THIS IS STANDARD PER ADC)
Build (Personal preference):
OR 
Jinx pro's:
- Q Not active is an attack speed buff per auto stacking up too 3 times, Active is a slower auto with splash
- W Single target slow with no damage early but okay damage late
- E AoE traps that explode over time applying a DoT
- R Global skill shot with missing %HP damage + scaling AD damage That is also AoE on impact of enemy champion
- Passive doubles your attack speed/movement speed stacking up to 4 times per champion/tower/inhib kill
- Attack speed/crit is great
- W and E keep her semi-safe in lane
- High base damage auto's
- Attack speed boost/wave clear Q ability pushes waves and makes last hitting easier
- One of the fastest tower taking ADC's (tied for first with Trist I believe)
- Team fight damage is silly good
- Hurricane with Rockets applies both AoE splashes
- Can 1v1 75% of the ADC's even if behind a little
- 1 full item power spike (BF with hurricane can win team fights because of your rockets)
- Hyper carry late game. (Full item jinx fed or not can win a game from any team fight late if played right)
Con's:
-
No real Escape
-
VERY position reliant
-
higher learning curve
-
weak laneing phase against fast pushing champs (like Cait)
-
Mobile champions/ Assassins like LB, Talon, Rengar, Zed See her and laugh as she lays on the floor crying for mercy, but mercy never comes as they continually force themselves upon her and her trusty guns... She screams for help, but the supports already dead, the top laner's TP was canceled, and the midlaner is farming mid lane instead of following their lane to help. All you wanted was to CS, but you forgot to ward, your support died trying to ward for you, and now you're here... begging.. PLEADING for your sorry excuse for a life you call ADC. As they continually smash their keyboards applying mark after mark on you... the light fades... you see nothing but darkness swallowing you whole. Your body in tatters, your mind shot, the shock doesn't even have time to kick in. You saw them coming, you couldn't run... there was NOTHING you could do... it was all over... the worst 1.7 seconds of your life.... That didn't even have time to flash before your eyes... RIP Jinx.... We'll see you in about 25 seconds when you re-spawn.
-
100% skill shot reliant
-
Can be easily kited
-
Champions/items that reduce attack speed hurt her hard. (Nasus, Frozen heart).
-
if not ahead early, takes a sadly long time to ramp up to mid/late
Summoners: (SAME AS CAIT YOU SILLY THING)
Build: (I have two ways, but the best one is):
Hopefully this helps you out somewhat, I'd put more... but I have to be up in 7 hours for work! Good luck on the fields of justice and if you have any more questions you can always add me in game
IGN: Xx2TailsxX
I'll help as much as I can! [slayer-jinx-catface]
) just to name a few, it's harder to actually carry from a tank position. Because assuming you're doing your job, you should either be dead mid-end part of a team fight, or you should be close too it.