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.
At level 7, you will want to have 3 Draconic along with 4 Abomination. This will allow you to find extra copies of Zyra as the game progresses. You can also use 5 Draconic, but if you start losing, you will either need more 3 stars or replace them with stronger untis.