Level up to 4 early if you want to start a win streak. Level up to 5 to try and continue the streak.
If you're weak in the early game, you can opt to save gold and lose streak instead.
At Round 2, level up to 6 regardless of your start. Put together the strongest team you can.
At Round 1, level up to 7. Roll down to stabilize your comp if you are weak. Afterward, save up to hit level 8 and complete your comp.
You will want to make Vel'Koz fire toward the enemies main carry. He will shoot toward the middle, so if they enemies carry is ranged and in the corner, you will want Vel'Koz to be in the opposite corner.