Katarina is a champ, which is kinda weak in the early laning-phase.
Why should I build this?

Especially if we think about playing against champs which can poke you with their auto attacks.
-the early Doran's Shield gives you the sustain you need to survive the first minutes.
-the teleport is a great opportunity to get some kills/assists on botlane. It also gives u bonus sustain on your lane.
-I choose movement runes, because you will often have the problem, if you play with smartcasts, that you never can imagine the range of your E. It helps you to get to your target faster and to survive lane ganks.

And Katarina is a RESET champ. Which means: GO ROAM AS MUCH AS YOU CAN!
Leave me a vote!

-Farm with your Q, W and auto attacks. Farm as much as you can with your auto attacks, which means, do it as long as it is worth. Taking too much damage does not replace this 20 gold.

-In early laning phase, you have to learn that you have to let some minons go, because you would take too much damage.

-After getting haunting guise, you can start clear ghost and wolf camps.

-If your target is next to you, use your Q-W-R. Then follow it until your W's cooldown is up and follow up with a E-W combo to finish it off.

-Use Katarina as a cleanup champ. Dont jump into a teamfight as first. Wait for the right moment and get your resets. While this, poke with your Q and W as much as you can.

-Use your trinket on lane with your E at ganks to get into safety easily.