Leave a liquid such as water on the leaves, and the succulent will burn if the light catches it. If you're using leaves, ensure that you get the whole thing. It is important to also take the rest from the pot. Fungus gnats like moist soil with lots of decaying leaves and plant matter, so if you keep your plant's pot clean and dry, they're less likely to make it their next home. Soil is a key factor. And that part is important - you want to ensure that all of the soil is completely wetted. You shouldn't use more water than is necessary to penetrate the soil.