Scrying is one of the best forms of divination for a sea witch to use. Scrying can be done in a bowl of water, into a body of water, or using a mirror.
For any of these, the method is much the same:
Slowly pass your hands in front of whatever you are scrying in, focusing on what you would like to discover.
Your left hand will cause the image to form, while your right hand will strengthen the image, though this will be reversed for left-handed people. Begin with your left hand, palm down, and alternate hands, gazing until an image begins to form. This may take time and practice, so be patient. Remember to blink; staring unblinkingly will only give you eye strain. Keeping your eyes just out of focus will often help greatly.