So Jesus answered and said to them, “Assuredly, I say to you, if you have faith and do not doubt, you will not only do what was done to the fig tree, but also if you say to this mountain, ‘Be removed and be cast into the sea,’ it will be done. And whatever things you ask in prayer, believing, you will receive.” (Matthew 21:21-22)
So it is not about repeating vain prayers. It is not about memorizing scripture. It is not about doctrinal correctness. It is not about anything that I think at all.
It is about being single-minded in focus, desire, so that there is no room for doubt.
What causes you to be unsure? That is the enemy of your prayer. That is the enemy of your performance in God.