He might start by training his aim constantly. Just like how he trained to be a ninja, he'd practice shooting at targets day in and day out.
Naruto could use his chakra in unique ways. Maybe he'd infuse his chakra into the bullets to give them special effects like increased speed or homing ability. This would be his way of adapting his ninja skills to his new sniper role.
Well, Naruto is known for his determination. He would likely study the art of sniping thoroughly. He'd learn about wind currents, distances, and angles, much like how he learned about different jutsu as a ninja. He'd also need to get used to the new equipment. The sniper rifle would be very different from his kunai and shuriken. But with his positive attitude, he'd gradually master the skills required to be an effective sniper.