I have finally figured out how to improve my focus/memory in prayer: Pray more
Focus or praying is like a muscle. If you work it out enough, it will be stronger. I stumbled upon this by coincidence. My sister died 4 weeks ago because of cancer. I have been occasionally fasting and praying in her behalf just in case she forgot a set of prayers during her stay in hospital.
Me and my brothers just did that. I have noticed my memory and focus improved and i became good at remember and know what rakah i am in.
My life is now better spiritually.