1. One flex field per “page system,” not per widget
Give a post type a single flexible field that represents the ordered body of the page. Nested flex inside every layout invites chaos. If you need sub-structure, use repeaters or groups inside a layout—not a second flexible field unless the information architecture truly demands it.
2. Name layouts for the editor’s mental model
Labels should read like story beats (“Lead with proof,” “Three-column features”), not developer shorthand (“Section type B”). Add short instructions in the field group description so new editors know when to pick which layout and what “good” looks like.
3. Constrain the menu
Every layout you add is a design and QA surface. Hide irrelevant layouts per template with location rules, or whitelist layouts for specific post types. Consider min/max rows where it matters (e.g. one hero, at least one CTA block). Fewer, sharper choices beat a fifty-item “add layout” list.
4. Match the theme to layout keys
In PHP, map each layout’s name/key to a partial or block render callback. Keep presentation out of the field definitions: fields hold data; templates decide markup. That separation makes refactors and headless exports far less painful than inline HTML stored in the database.
5. Performance and migrations are part of the model
Heavy galleries and relationship fields inside flex rows can multiply queries—plan lazy loading, sensible limits, and object caching where needed. When renaming or removing layouts, script data migrations or compatibility shims so old content does not silently disappear on the front end.
Flex fields shine when they implement a shared language between design, development, and editorial: a finite set of well-documented sections that compose into complex pages without sacrificing consistency. That is the difference between a flexible CMS and a pile of one-off hacks.