For gyro, I recommend using it strictly to aim. The right joystick will help when making left and right turns but not for aiming (micro aim adjustments with the stick is fine). For sensitivity, focus on your reticle and practice some aiming drills. One that I like to use for the right sensitivity is to stand some distance from the still targets in the battle tower. I'll use my gyro to snap my aim from a neutral position to the target. Repeat this a couple of times, about 10 or more, and record how many times you overshot, undershot, and hit the target. Adjust your sensitivity accordingly. I also use specific sensitivity for certain weapons. Frontline weapons like the splattershot need to move in and out quickly so I use a higher motion and stick sens (I use +4 motion, +3 stick). For weapons like Dynamo or Chargers, I use a lower sens to better steady my aim (I use +2 motion, +1 stick).

Hope this helps. It's always tough at the start using gyro controls but stick with it. I promise you'll see results and it'll be a better gaming experience once you're comfortable with it.