Help get everyone in shot, including yourself, by using the timer option. When using the Camera app tap the timer icon at the top (it looks like a clock face) and choose a 3-second or 10-second delay. Prop up the tablet and press the take picture button.
The LED flash (if the device has one) will illuminate to indicate the countdown. It then takes a burst of shots to ensure you get the perfect one. You can look through them afterward to pick the best.