You need to be cautious because your mind at one time can get you to Heavens, the other time, if you are not careful, can take you to hell.

As much as you can, try to concentrate your mind to good thoughts, holy thoughts that sanctify man.

[…] It is initially usual for our mind to leave during prayer.

With persistence it becomes bound to God and it won’t separate from Him, it will want to pray continuously.

After that, a complete deadness comes, no thought whatever appears in the time of prayer, our mind remains empty.