Tilting pelvis forwards to activate the deep trunk and pelvic floor muscles
Sit on a chair. Tilt your pelvis forward so that your back curve increases. A good posture will make your pelvic floor muscles activate spontaneously. At the same time lightly pull in your lower abdomen and if needed tighten your pelvic floor muscles a little more.
Try to sit with the pelvis and back in a neutral position (weight on sitting bones) or if possible pelvis slightly tilted forwards (weight in front of sitting bones).