What are the most common mistakes made when cloning marijuana?

Thanks for the question. The two most common mistakes are too much light, and an improper balance of moisture in the medium relative to the amount of venting in the humidity domes. Usually, trays are overwatered, which poses a risk for oxygen depletion. If you keep them around 4lbs, keep the ambient temperature of the space around 73 degrees, and use a heat mat to warm up the root zone to 80, you'll get convection heat that causes the moisture in the medium to "cook" out the moisture, which creates humidity in the dome. If you don't have enough holes in the dome, the tops of the clones will yellow out from being too wet. Cut enough holes in the lid to just have a very slight amount of condensation in the dome. Keep the light level down to 50-60 PPFD. Any more that that will stress the clones. When they are rooted, you should increase the light to 80-100 PPFD at first, wait to see some healthy growth, and then increase up to 150 PPFD. Especially with LEDs, the transition into bright light needs to be done in relatively small increments, and then wait 5 days to make sure the plants are healthy, then increase again.