When organizing visual aids in a technical document, it is best to avoid visuals that:
a. echo information from the text.
b. appear in the middle of the document.
c. are surrounded by a lot of white space.
d. don't have clear captions or labels.

I would say that they shouldn't be surrounded by a lot of white space and should have clear captions. The question of white space is one of good presentation so the visual looks like an integral part of the whole topic and having clear captions is so that the visual is well explained what it is.