Actually, that's the 'old school' way. Training today usually teaches the Harries Technique if you're using a pistol or a weapon-mounted lamp if using a longarm. The mistake most people make is clicking the lamp on and leaving it on - thereby attracting fire. You're better off using flashlights with momentary-on buttons and 'flashing' the lamp on and off quickly, like a flash bulb. Flash it on and off - and then move.
The Harries Technique was created by the late Michael Harries. If you're right-handed, you would hold your pistol in your right hand and your flashlight in your left, with the head facing away from your thumb. Hold you right arm out as you normally would and bring your left hand, with your flashlight, under your right with the backs of your hands touching. You would then use your middle finger to turn on (and off) your flashlight if it's switch is on the side, or use your thumb to turn on your flashlight if it's switch is on the rear. The Harries Technique allows a more secure two-hand hold while still being able to use a flashlight.