Hi. I'm a brone feeder... I mean a bronze. Sadly I know well the game but I have a lot gameplay mistake. (skillshots, greed etc.). This build is not a tier 1 challanger build but it works AND fun. Sometimes you need a bit fun to refresh yourself after a hard game so there is your chance: Lethality Caitlyn.

Be sure to get a friend or someone who can carry you if you fail to. (also you can laugh with them if you oneshot the enemy adc with your ultimate) If you can't make the runes while picking champion make it before the game. Also an item set made before game is good.

This is my choises of runes. I have some bad habit I know and I am working on them.
Dark Harvest - Predator: Both are good. Dark Harvest is a lot better in mid and late game.But Predator can also be good if you keep your boots.
Eyeball Collection: I usualy use this one becouse I can't make the most out of the others. Anyway feel free to choose the others.
Ultimate Hunter - Ravenous Hunter: Both are good. Use Ultimate Hunter if you have lifesteal (of you don't want to have) becouse it will make your ultimate reload faster and your ultimate's damage is usualy huge anyway. Ravenous Hunter is good if you need that bonus lifesteal from abilities (your q does a lot of damage both earlygame and lategame)
Second rune tree: It can be anything. Precision give you better DPS. Sorcery give you damage, mana or mobility (I run out of mana most of the time so I nearly always use Manaflow Band) Inspiration is special. It can be used very well and it can be used very poorly. It depends on you.
Stats: Adaptive stat if you want a better early and attack speed if you want a better late game. The last is usually armor or magic resist. (it depends on your enemy)

Doran's Blade: Standard starting item, it helps you to stay in lane and also do some damage.
Cull: If you think you can't kill your lane but you can farm better your choice is the cull. It will speed up your early game even if you do not get kills.
Doran's Shield: If your enemy is poke oriented Doran's shield is for you. It help you alive the poke damage.

Health Potion: You will need it in early game to replenish your health.

In early game you don't want to fall behind. If you can get fed that is good but if you fall behind... you will be a sitting duck. I recomend you to poke with q at 75%-80%+ mana and shot as many headshot into the enemy as many you can without missing farm or geting damaged too much. At LvL 6 you can be more agresive to get your enemy low enough to kill it with ult. (or fire I don't judge) If you can't do this (or your enemy can dodge your ult eg. Yasuo w, Vladimir w) you can roam to bot or top.

Your primary goal to get fed. With 1-2 item your damage is up in the skyes. If you get ahead in early you can easlily one shot your enemy with a good combo. (I recomend the Headshot-E-AU-Q-Ult combo) Also the infernal and mountain drakes are targets. (Ocean drakes are good too in early/mid game. Cloud can be good also but not a primary target.)

Infinity Edge: This is your 5th item usually. This will give you a chance to deal insane damage with your headshot.
Rapid Firecannon: This will help you to outrange the enemy ADC and mid.
Essence Reaver: If you use up too much of your mana and you want to replenish it you can buy this. But most of the time you are good with mana this late.
Phantom Dancer: If you are afraid of geting one shoted but still you want that crit than this is your choise. It give you shield that just enough to you to combo on the enemy and burst it down.
2nd Infinity Edge: With the core build and 2 Infinity Edge you can deal a ton of damage with a headshot if you are a bit lucky. (50-50)

Bloodthirster: If you are die a lot and you need only a little lifesteal to survive than usually this is your answer.
Death's Dance: If you use more of your spells you can buy this instead of The Bloodthirster. (and The Bloodthirster AND this if you want that much lifesteal)
Maw of Malmortius: If you get killed my AP bursts you can save yourselft with this one.
Black Cleaver: If ther is a ton of armor you can buy this and penetrate that with a Black Cleaver. But if there is that much armor than your team's APs are have a good time (If there is any. But why you are picked AD then instead of AP?)
Mortal Reminder: Mortal Reminder is a good alternative for Lord Dominik's Regards if there is too much healing on the enemy team. (Soraka, Mundo etc. we know them well)
Boots: Yes. You can buy boots. But be honest: if you are playing lethality caitlyn you are nearly trolling. So who cares about boots then??? (Anyway good boots: Berserker's Greaves, Boots of Swiftness, Mercury's Treads)

Now you are at near full or full build. Usualy you can oneshot the adc and mid. Your ultimate is at least half of their hp. You succesfully became a glasscanon. I'm so proud of you. Don't forget the dragon and the baron! And hunt down that adc. (becouse usually you can do it easily)

Pros:
-High one shot potential
-High range ending even from higher hp
-Fun
Cons:
-Low dps
-If you fell behind you will have a hard time
-Low mobility
-Champselect will be dodged at mid sometime becouse of "trolling"

This is my first guide so I would be happy if you write a comment about what can I do better in guides (I know... I have to get out of bronze...) Also feel free to vote it up OR down! I know that I have to get better in both guides and gameplay.

Bye!