EPTI go 21/9/0 with ghost and flash. I feel that with E and traps you should never be caught entirely off guard so you should be able to use your summoner spells sparingly.
My runes at the moment are AP reds/quints and Mana regen yellow/blues.
This allows me to be able to continuously use my skills throughout the laning phase without drowning out of mana any time soon because Caitlyn can do a lot with just one of her abilities such as clear a wave, trap a bush or have an escape ready.
Anywho, the build. I usually go Blade, Zerkers/Treads, BT into IF however I feel that although the damage is great for her abilities I just think it trails off for auto attacking like in team fights. Although you should be on the outskirts of the fight just poking from safety, I think that instead of the mass damage of let's say I have a BT at the time, maybe a Ghostblade/Bruta would be better so I can spam the Q harder and have E a little quicker plus it does a fair amount of damage anyway plus even more armour pen.
However I got a shitload of coursework to do so I shouldn't play any time soon :[
