this is in my opinion the best way 2 play Kalista, some will say i'm wrong, but this is how i play her (with great succes).
i hope it works for you 2. GL HF and maybe i'll see you ingame!

the skill order is pretty self explaining. max Rend (e) first, then Pierce (Q) and last but not least Sentinel (w). this order because your damage potential will be maxed out durring the game.

the reason for BoTRK first is because your dueling potential is better in the laning phase. next are the berserker greaves and runaan's hurricane. the order of these are not very important, it's just attack speed and a bit of extra jump-range.

then for the lifesteal and damage. or a bloodthirster or an essence reaver. if you're out of mana a lot, then u get essence reaver otherwise you shoul always get bloodthirster.

for defensive i recommend the mecurial scimitar and then the infinity edge. the rest are defenitly situational.

durring the early laning phase, play very defensive. your damage and mobility is very limited. however if you get a good gank or some early attack speed you can be more agressive..

if you get ahead early then BE agressive, or you will fall behind eventually.

when you get to the team-fight phase, be on the backline of your team. only use the hopping from side 2 side, not forward, you will likely die if you do.
group when you want, but remember to keep farming. you need a lot of cash to stay/get ahead.

then the siege phase. focus the turret and hop around a lot just to make the skillshots miss.
if your on the defensive. jump around under your own turret while harrassing and wave clearing.

during baron and dragon fights good posisioning is a must.

make sure you always have one side control, if they come from both sides bet in the pit and flash over the back wall. otherwise stay in the opening and kite back when it gets hot.

make sure you auto-attack the drake/baron as much as you can, jsut so you can secure the objective with Rend (e). it's basicaly a second smite :)