I do not see where the Bible commands us to visualize when we pray. There are passages in the Bible that describe things in detail, the tabernacle for instance, or Ezekiel's vision early in the letter, where there is a lot of detail to describer the events. Some people who are familiar with the terms and colors there may be able to visualize these descriptions in their minds.
Back in the 1980's, there were people teaching the idea that visualizing when you pray is important. Another man, Dave Hunt, came out with a book against visualization. I do not even recall his arguments. My recollection is that they seemed extreme. I have read some commentators calling visualizing the Lord 'idolatry.' That seems a ridiculous leap, especially considering that some people who read Revelation will imagine the vision they are reading, and there is no command against thinking in pictures.
Some people do think in pictures. If you say, "red banana' they will clearly see that in their minds eye. I barely think in pictures at all. A lot of my dreams are like moving paintings or cartoons, not as clear as real life. I cannot easily build an outbuilding in my head. Some people can. I think in words and concepts. I am higher on the verbal end of things and lower on the pictural end. Some people see a picture in their mind when you say a word. It is how their mind operates. If doing so helps them focus when they pray, great. There is no command against visualizing when you pray. If someone else prays without seeing pictures, fine. The Bible teaches neither for nor against....as far as I can tell. If it does addresss the subject either way, please let me know.
There is also the issue of God showing visions. He gave many prophets visions. Jeremiah saw a boiling pot and a branch of an almond tree. He might have been walking around and the Lord spoke to him as he saw physical objects. Or the Lord might have just dropped pictures into his mind's eye. Or he might have been in some kind of trance where he saw objects that were not physically present. This is different from just imagining pictures in your mind.