UXGuide

The UXGuide gives user experience interaction guidelines for Windows. This document is very useful for any UI developments. For more background information to help you improve our labels, read the chapter on Text. Both the User interface text section and the Style and tone section give you a good insight in how to write proper text for UIs. The chapter on Messages also gives some information on what proper text is.
Also have a look at the user interface development guidelines for D365 FO and D365 BC.