The speed and handling of the La5 lets you saddle up nice and close - 200-ish. That's where to set convergence. The ballistics and rate of fire the guns have are not good, so
don't spray and pray. The slow rate of fire can actually help you because it lasts for a lot of kills. If you get within 200, just start tapping the trigger until you connect. Then pieces start flying off and finally that spixteen plummets into its well deserved final resting place.
Oh, and watch out when in a fast dive. You'll need to add in some down elevator trim when going really fast as the plane tries to lift on you.