Imagine an invisible boundary, perhaps a circle, which extends around you. Now determine a series of responses should anyone cross that line without permission. The next choice might be to move back or to the side and recreate the distance. If that fails running is always a useful choice. Finally, knowing how to place the appropriate knee might be useful.
Physical attack is always the last choice but in no way is it an inappropriate choice.
But knowing your physical perimeter is extremely important. Likewise know your emotional perimeter. What information are you willing to give and what information is private. All too often people seem willing, or even feel obliged, to answer questions even if they are personal and private. That information is only earned by people you have come to trust.