This is going to be different based on the type of apron you’re using. But in a general sense, these are the steps to ensure you’re correctly tying most types of aprons.
Put on your apron so that its front surface covers the front of your body, adjusting based on where the apron falls.
Bring the waist drawstrings to the back of your body and tie them in a bow around your waist. If you find the strings are too long, cross-tie them behind your back and bring them around the front to tie the bow.
Pull the knot tightly, making sure to tug on the apron to ensure it fits properly and stays on.