The only reason you want to play Kalista support is to DOMINATE the early laning phase level 1-5. She is currently the most lane dominant champion that you can play.
Our main objective is to Zone enemy and give your adc as many space as possible. Your aim is to give your ADC a CS lead and take kills for early dominance
In the mid - late game your goal is to Control Objective and Bail out your ADC. Your UltimateFate's is the best tools to secure your adc from dangers and your damage are suprisingly decent to kill off their squishy members.

If TWO conditions below met your Game Condition

• Your team commited on Poke comps or Need more Damage

• Your ADC is long range(lane bully) - immobile champion (Varus/Ashe/Cait/Draven)

• Enemy picks pick weak early game support

• You're just a Kalista Main and want to inflict pain

if you are familiar with / / Support. This might be a easy answer Deal Damage.
While Ashe could provide you with a super strong engage Fate's, Kalista provide you with Disengage (or possibly engage depend on how you use it)
Trading guide: There are a lot of guides on other channel on how to play Kalista. The most common trading pattern I always use are AA-Q-AA-E.
Most cases just pokeing using Q-E is enough for poke and slows .
Since you are maxing Q with lethality build, poking Q could deal quite a lot of poking damage, keep throwing your Qs!!

Early game

This phase is the most critical point of the game. Depending on how you or jungler perform, this could determine the outcome of the game

• Walk directly to Bot unless team asking for invade.

• Force trade enemy support/adc lvl 1 (this needs a lot of practice) Trading Sums are very favourable in almost every cases

• Remember to AA enemy champion for trading with your ADC, your W passive will provide extra damage if your Soulbound attack the marked enemy

• Help your adc push your wave and make sure you have the pressure at all time

• Help your Jungler take Objective (Dragon or Grubs) your [icon ability=Rend size=50 are super good for securing objectives.
  *Tips: Around min 5:10-5:40 try recall and walk mid. If enemy jungler is on Bot side, rotate top and ping jungler to take grub (vice versa).
  If the condition is not suitable, just look for ganks/help mid push and go back to your ADC*

Mid game

Your current goal are to clear vision and help your team to execute a mispositioned enemy (remember Q-E to slow if you need to chase). You are not an ADC, do not forget to ward, take cs if your laner do not catch the wave (classic soloque). Warding should be easy cos there you can wall jump around the maps using you Q.
Your task is to catch a mispositioned enemy, DO NOT OVERCHASE. Kalista strength is her mobility.
While warding are essensial part of your Role, keep your ADC in checked. Remember your R could bait important enemy spells and a jail free card for your adc.

Late game

Same as mid game, but stay close to your teammates and adc more, since one mistake could be fatal. During posturing for securing objective, stay away from enemy CC as possible. You have to be alive to save your adc.
During fight, target keep kiting and deal as much damage as possible.