To do the Dead Bug, lie on your back with your legs out straight and arms overhead. Crunch your shoulder blades up and lift your legs up off the ground as you press your low back down into the ground.
Then bring one knee in and lower the opposite arm down so your hand is pressing into your knee. Keep your arm straight and press down on your knee as you press your knee into your hand. You should feel your abs contract extra.
Pause then switch, bringing the other knee and hand together as you straight the opposite arm and leg out. Pause there then switch again moving slowly. Try to really create tension as you push your hand into your knee.
If you feel your low back engaging, kick your legs out higher instead of keeping them close to the ground. Also, make sure to engage the glute of the leg extended out. Beginners can instead bend both knees, tucking one knee in as the touch the toe of the other foot to the ground. See below for a beginner option.