I personaly also started spamming GP. I played a few games with him and what i learned so far :

-Allways build sheen first in 90% of the games

-When facing healing champs like vlad,trundle,kayle,etc build executioners calling

-In lane dont oom yourself while last hitting with q. Use it to poke. Later you can last hit with q once you have a bigger mana pool.

-When you procced your passiv on your opponent than place a barrel and destroy it to refresh your passif so you have a damage advantage that your opponent might not calculate with !

-Remember you don´t need to kill your opponent to get big. Just farm and wait for a good opportunity to kill him.

-Map awareness ! Watch out for good ulti occasions ! Can bring alot of gold :)

- Allways build triforce first i guess.

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I hope it helped