Everybody has weak points
There are universal soft spots on every body type that you should aim for, and there are certain strikes that are safer for you to use than others - so you don't injure yourself.
Using your palm strike to the temple! The bottom part of your palm is extremely strong. Keep your fingers together, put your hip power into it, and strike. Keep your other hand up to protect your face. FYI palm striking to the nose or chin are also options.
Use the top or bottom part of your elbow to strike at the jawbone.
Even those with muscular stomachs have a vulnerable non-muscly socket right where their rib cage branches open. Use your elbow and jab backwards!
Use your *hip power* and drive your knee up!
Okay listen up: knees break easily. Pick up your foot and stomp through their knee. (Also try to aim)