I wrap my hand around the back of the head with my thumb on one side and index finger on the other. Use a fingernail to pull up on the tip of the top beak and then use the thumb and index finger at the corners of the beak to hold it open while you give it. This helps stablize them if they struggle or try to get loose, you can also use the same arm that is holding the beak to hold them against your body and keep wings from flapping. I usually have them in my lap while doing this, but you can also have one person hold while the other does the meds. When they are are larger and have wattles you can sometimes open the beak by pulling down on the wattles.