With valla I focus around Lifesteal. Combining her high attack speed with 45% lifesteal and searing attacks' 50% bonus damage she can even tank boss mercenaries!

Valla is usually a safe pick, 1st or 2nd, so I don expect to counter anything, just give a ton of DPS to the team while not needing a good healer to keep me alive.

Before level 4 I play full defensive and not trade at all

After level 4 I'm looking for chances to trade damage and try to force at least use of the wells for the opponents

After level 7 I get my main lethal, searing arrows. At this point I am trying to bait enemies to commit to fighting me and then activate searing arrows and hungering arrow to burst them down.

On level 10 comes the 1st question: Should i go strafe? Strafe is only good against targets with low CC and/or high mobility, like tracer, li ming, illidan. Otherwise, Rain is the way to go. Going strafe means half of the teamfight I am not using auto attacks so both giant killer and discipline are useless so I am going with spell shield instead.

Another question comes on level 13: Do I need Giant killer? Giant killer gives a damage boost, but this is unnecessary if the enemies do not have high health offtanks(sonya) or non-tank heroes(azmodan). Even against 2 full tanks Discipline is preferred because the lifesteal outheals their damage, and stoneskin is easier to use in the heat of battle because you do not need to target anyone. Using Giant killer means losing 30% of the 45% lifesteal of the build so Blood for blood is an alternative source of lifesteal.