Second, you rule your mind, it doesn't rule you. But instead fighting the thought, just shift your mind to something else, i.e. the meaning of your prayer.

You cannot control (entirely) which thoughts will enter your mind. But you can decide which thoughts you actually entertain and dwell upon.

Another thing you can do is limit your exposure to things that would trigger strange thoughts. And finally, say a little prayer for yourself, asking G-d to have mercy on you. But the main thing is, don't let it get you down. Don't think: "If I'm having these thoughts during prayer, my prayer must be worthless." That's a mistake. Actually, because your prayer was going well, and you were doing some fine spiritual work, the "other side" kicked in and tries to challenge you.