Duration of stay

I need help on my situation. I applied for for visitors visa to the US. When i filled in my application,i requested for a month and i was given a 2 years multiple visa.

I know at the port of entry it’s the immigration office that determines one’s stay. I would now want to stay for 4 months incase the officer gives me 6 months. I don’t plan to over stay and ruin my travel chances. What should i do not to ruin my chances but still also stay for 4 months? Can i book a ticket of one month then later extend it for 4 months? If i stay 4 months won’t they think i am not truthful the next time i apply for a visa? I am confused.

I will appreciate your response.