Nav bar, or other one dimensional content?
Flexbox is good for laying out items in one direction - usually horizontally, but vertically as well.
Grid of items, or other two dimensional content?
Grid is good for whole-page layouts, as well as any components that require structure both horizontally and vertically.
Images or elements that text should flow around?
Floating an element allows subsequent elements in the same container to move up and flow around it. Elements can be floated to the left or right, and they must be "cleared" to prevent breaking the layout. See lesson page for details.
Elements or images that should sit in-line with text?
Inline or inline-block display