1- Sometimes certain sins cause us to struggle with prayers. If this is applicable try to stop them as best as you can.
2- Sometimes we don’t fully accept God’s system, or something happened and we are upset with God for letting it happen. If this is applicable try to overcome it.
3- Talk to yourself before praying. Psychologically it’s very impactful. Tell yourself: I will now pray just like the Prophet (s) prayed and just like Imam Ali (a) prayed. I’ll just stand and thank my Lord. That’s it. Sometimes mentally simplifying it helps.