Is it permissible to read salah with your eyes closed as it helps me focus. Also what are some tips to improve your salah? What can I visualize when reading salah to help me focus. I heard Ayatollah Khomeini said to visualize a bird and concentrate on keeping it on the tree and prevent it from wandering off. Would you recommend this?

Yes it’s permissible
You will need to do many things to gain that focus
This books helps:

101 Ways to Concentrate in Prayer