First i want to said: If You read this chapter, You don't be pro, but i think it will be halpfull to do this.
Second im not pro player.
And the last one: i play couse i like it and its fun for me.

I choose this couse i think its the best for this champ, but u can change it :)

Items always are the most imprortant thinkk in Yours game. As i write, first i buy Doran Blade, second Berserker's Greaves, third item is Vampiric scepter but its not importat what u buy first: Blood Thirster or Black Cleaver ( i prefer Black Cleaver couse it's aditional AS) than Phantom Dancer ( it is very halpfull if u need to escape from "gang") and infinity Edge - but what when it's isn't end of game and u got to much gold? Sale Doran Blade and buy somethink what help u play against Yours oponent, or somethink to incress Yours HP: Frozen Mallet or Warmog's Armor ( first give u HP and slow - incress Your chance to kill escaping enemy, but Warmog give u more HP and regeneration), after that i sell Berserkers Graves and buy second Phantom Dancer - yes i'm slower but AS is somethink like 2.0, after that i buy elixirs.

U MUST REMEMBER: You got one of the best range, and it's your main attribute.
Before u play normal games go costum to learn about Your skills, couse it's can change everythink. Q - skill got very good range, and demage, W - skill is use wery seldom, couse trap is easy to spot, but u can grass, E - skill is important, not because it slow enemy, but it move u back and u can move through some wall, and help when u need to escape. R - skill is useing to KS or finish a enemy. It got very large range but can be blocked. When u play mid, and u know your ally died fighting with oponent go to help him, even u late u can use R - skill. U must remembet than you are Caitlyn, and opponent focused u, than stay behind all ally. U got much DMG and range and AS.

I believe i help somebody, and i apologize: because im not to good in english, and i know there are much mistakes, sorry