First off, very much enjoyed the article! Thank you!
How do I gain mental power? By clinging to God . . . by clinging to truth, my mind thinks most clearly. What is an evil thought? For me, it is something NOT Loving . . . it is something NOT true. Would God desire one of His own to to hang to evil thoughts for any length of time? I think not.
When a mistruth/something unloving pops up in my head, I use DISTRACTION to remove it. Reversing the lie of my thought with truth. "Do not be overcome by evil . . . but overcome evil with good" are the words repeated in an old VBS song I use to teach children. Love it. Love YOU!