Caitlyn is all about attacking, repositioning, and attacking again. Combining her massive range and her damage, not to mention Yordle Snap Trap (hard cc on a ranged carry, albeit tricky to use), she can be a massive threat right from the beginning of the game, scaling into a full-on carry with an emphasis on cs.
Best laning partners: Alistar or Taric


Note: This is NOT a solomid guide. This is designed around ranked gameplay or premade duos of Caitlyn + support and thus revolves around a bot-lane Caitlyn.

With Caitlyn, I usually bring Flash and Exhaust. Both spells can be used either defensively or aggressively, a duality that I appreciate very much, due to the unpredictability of LoL games.
I recommend always using 90 Caliber Net over Flash in order to save the more costly summoner spell as a secondary gap closer (or farther) so that you can cover an enormous distance very rapidly. In case you require a rapid escape or gap closer in order to flee a gank or quickly shut down the distance between a rapidly fleeing enemy travelling faster than you, then proceed to use flash first, since 90 Caliber Net requires a short channel time that could be costly.

Regarding Exhaust, either rapidly close the gap between you and fleeing enemy using your traps and flashes, then exhaust them to give your team some time to catch up and crush an enemy that you cannot kill alone or exhaust any champion (usually melee) that jumps on you at the beginning of the fight, followed by a quick flash (preferably with 90 Caliber Net) at which point you can kill them from a safe distance. It is usually worth it to simply cast exhaust over any large threat on the enemy team during a teamfight if you consider yourself out of harms way. It could potentially save a number of lives on your team, instead of just yours.
Flash allows you to dip in and out of a fight, exhaust allows you to temporarily shut down an enemy of your choice in terms of damage, cleanse allows you to break free of any all and cc and now ignite, ghost also allows you to dive in and out, but with an overall different effect that in certain situations can be considerably stronger than flash. And finally, teleport allows you to quickly enter a teamfight no matter where you are on the map, providing you with much-needed large-area mobility.
While not generally recommended, any of these three summoner spells could be used at the cost of some of your dominance in the game. Promote will allow you to push a lane just a little bit harder, which could be useful in the event that both teams square off in mid lane (a common occurance, especially at lower ELO play including and up to 1200-1400). Heal could possibly save you the trouble of recalling after a fight or just plain save you in a fight. Ignite, I don't recommend simply because it takes the place of a spell that allows greater mobility and it's usually brought by someone based around cooldowns like an AP champion or aggressive tank, although it could be viable depending on your opponents' team and your personal skill level.

Alright, simple enough. Your basic 21/0/9 AD carry mastery page with a few variations. I take the utility tree because placing Yordle Snap Trap, using 90 Caliber Net, followed by your ult begins to consume quite a bit of mana.
After that, taking Swiftness is simply an added bonus I like to bring a long to compensate (slightly) for Caitlyn's terrible base movespeed sans movespeed quints.

Other than that, adding points in critical damage, attack speed, armor pen, and that 3% bonus lifesteal simply makes her that much more of a threat.

Armor penetration runes, really allow you to boost your base damage with that first doran's. While a new popular build involves Boots of Speed] + 3 [[Health Potion (very tempting for the low-movespeed Caitlyn), a Doran's Blade + armor pen and a bit of extra damage from the Seals and Glyphs of Malice allow you to not only pull off easy, yet painful harrassment on your enemy laners from maximum range.

Furthermore, as your base damage begins to scale (per level), your passive ( Headshot) actually begins to visibly heal you when used upon a minion (in my opinion, why use it to harrass at only 50% additional damage when it could heal you and you can simply harrass with normal attacks?).

I understand that rune pages aren't easy to set up and regarding that, my advice is to simply mix together anything you feel is viable or that complements your playstyle and chug away at your opponents.

I'm not a big fan of per level runes simply because I like to focus on my early game in order to scale into late game, but you should definitely give it a go and let me know how it works out.

I start with a Doran's Blade Doran's Blade because, as I mentioned earlier, it combines with your base armor pen, damage, and range to provide easy yet painful (for the enemy) harrassment and allows you to heal off minions with headshot.

Following that, I usually attempt to buy Berserker's Greaves Berserker's Greaves and a B. F. Sword B. F. Sword on my first trip back. Failing that, I either buy Boots of Speed Boots and my B. F. Sword or simply my Berserker's Greaves.
I strongly discourage buying simply the B. F. Sword, since your laning phase shouldn't last much longer and that alone will not serve you in any teamfights.

After a bit more laning, finish up either your Berserker's Greaves and turn your B. F. Sword into a Bloodthirster Bloodthirster. This will help you sustain yourself in teamfights as well as give you a significant damage boost.

Quickly grab a zeal Zeal on your next trip back then begin working on your Infinity Edge Infinity Edge to help your damage along a little further, as well as draw in a reasonable crit chance and crit damage.

Following your Infinity Edge, go ahead and build a Banshee's Veil Banshee's Veil in order to max out your survivability with minimal damage sacrifice. The spell shield on it will prove invaluable in numerous teamfights, not to mention the extra health, mana, and magic resist.

By this point, the game should have progressed reasonably far and probably near its end, since you're probably carrying with this build if you've gotten this into it. Considering your damage, people are probably going to start stacking some armor to counter you, so grab your last item, a Last Whisper for the armor pen, and your last bit of damage.

After finishing your build, use any extra money you have (although I recommend allowing your team members to begin racking up their own gold with kills so that your team can help you win this) to buy any and all elixirs. This includes Oracle's Elixir, Elixir of Agility, Elixir of Brilliance, and Elixir of Fortitude, not necessarily in that order. The small stats on these items are worth a lot more than you might think.

I start out with a point in Yordle Snap Trap simply because it provides excellent control of your lane early-game, enables you to protect your jungler and suffices for an early-game "ward" of sorts.
In fights, attempt to root melee enemies in place. This will limit their effectiveness in battle, provide constant vision of them, and it does a fair amount of damage. If your team seems to be handling teamfights well, then consider placing yourself more in harms way and attempt placing traps behind their team in order to prevent easy escapes for any of their team members.
I max Yordle Snap Trap second because of its massive utility not only during laning phase (closing off brush as well as a portion of your lane or snaring any possible gankers is extremely effective) but in teamfights as well. At max rank, it has an 8 second cooldown, but frankly that feels like nothing at all when you're engaged in a fight.

Right after that, I grab a point in Piltover Peacemaker and max it immediately. This is a large source of damage for you and is your only AoE (without building a tiamat's trololol) and it does a large amount of basic damage and scales extremely well off of your total AD. While it may seem silly, I strongly recommend holding off on spamming this every time it's off cooldown. It consumes a significant amount of time used for basic attacks (which, late game, begins to stack for a lot of damage) as well as a stacking amount of mana (which could be used for escaping with 90 caliber net or placing Yordle Snap Trap, not to mention it could possibly draw mana off, disabling your ultimate.

I grab 90 Caliber Net at level 4 and max it last because, if you play well enough, one escape or 2 (With Flash) enables you to fight from max range once more, especially since the slow from the Net discourages enemy champions from chasing your farther. Take note that 90 Caliber Net propels you a set distance AWAY from the direction in which you cast it, meaning that you should usually avoid casting it at fleeing enemies unless it will buy your team enough time to catch up and crush the opponent in question. 90 Caliber Net can also be used to propel yourself over small walls in the map, and thus enable a quick and easy shortcut across much of the map.

Concerning Ace in the Hole, I have a large problem with amateur Caitlyn players. DO NOT USE ACE IN THE HOLE TO BEGIN A TEAMFIGHT, UNLESS YOU ARE ASSASSINATING SOMEONE ALREADY LOW ON HEALTH There is a reason your ultimate is called Ace in the Hole, does so much damage, and can be blocked entirely by an enemy champion. It is your Ace in the Hole. It is a finishing move and meant to be used to crush fleeing opponents. Charging the shot and possibly having it interrupted or intercepted by the enemy tank at the beginning of the fight is a huge waste of time and mana. The range for casting this is large enough that using 90 Caliber Net and possibly Flash is more than enough to get you within range of most ranged characters with ease. Spamming this spell is a waste of your time and certainly a waste of a valuable spell.
Now, obviously rank this spell at levels 6, 11, and 16, as with all ultimates. Charge this on fleeing enemies, most especially if there does not seem to be any other enemy champions, or few enemy champions nearby capable of intercepting the shot. Try and use it when champions are farthest apart without falling out of range in order to prevent enemy champions from interrupting its channel duration. The damage on this spell is often enough to finish off either your target or the one who mistakenly believes they can intercept it at the end of a teamfight.

To cap it all up, play Caitlyn as she is: a squishy, AD carry with massive range. Move between attacks to reposition yourself constantly in teamfights and make careful use of your traps to guard yourself or snare fleeing enemies, or even just disable melee opponents in a fight. Following that, use any of your spells and combine them in order to easily dominate in your next LoL game.

I wish you good luck.

If you have any questions or comments (hopefully good ones, though I'll graciously accept criticism) please rate my guide and leave a message below.
Cheers :D

Created:
12/06/2011 - Made original guide.

12/07/2011 - Edited Quintessence error, changed build from Infinity Edge > Bloodthirster > Bloodthirster to Bloodthirster > Infinity Edge> Last Whisper. Also edited BBcode for spell, champion, item, summoner spell icons. Edited Viable and Acceptable Summoner Spells.