Apart from using the proper colour constants for standard colours I invest some extra effort for applications that we need to use internally on high DPI screens, or where customers may need this.
I have a unit with helper functions for determining proper sizes and placement margins, which compute these from the default GUI font and the standard values in dialog units as given in the UI guidelines, and with helper functions to compute the maximum width / height of an array of controls, place controls, things like that. For fixed size forms and dialogs I calculate the placement of controls once after translating their text with GNU gettext, for resizable forms I do this in an OnResize handler.
This gives good results, is however time-consuming. I would like to have something like the wxWidgets sizer functionality, which automates resizing once the minimum size of a control is set. I have never seen something similar for Delphi, though.