When you first get Kalista you want to be aware of your passive mortal poise, this can be very helpful or very unhelpful if used wrong. What the passive does is that when you auto attack you can kind of jump/leap in a direction. When you do this you want to make sure you know where you are going and where the other team is. If you use this correctly you can kite or go aggro very easily, but if used wrong you could be just lunging yourself into the enemy line of fire.

When you farm watch out that you don't auto attack too early, this is because you cant cancel your auto attack when you have already clicked on the minion.

Other than that just farm normal and don't get too far ahead of your creep wave because you can take a lot of damage if you go too aggro.