Make sure that your saddle is in line with your frame! Look from above to check it

Once you have chosen the right height, screw again the nut using your hand and close the lever. You need to feel tension on the lever when you close it. If you feel it too soft when you close it, open again, screw on the other side a little bit more and close it. If it is too stiff, unscrew and close it again

Now you released your seat post. Move it up and down until the right height

Unscrew on the other side

Release the lever

Adjusting the height of your saddle