It all depends on how much information you need that is different between each of your classes. I have this problem quite a bit and play with my UI much more than I should. If you're just starting off, you can try a pre-packaged UI like tukui or elvui. This will look identical from character to character (but comes with all the warnings about using a pre-packaged ui that on patch days things can get hairy if that critical mod has not been updated).

My other suggestion for keeping things updated from character to character is to make use of the "profiles" features in most addons. Tweak layouts the way you want them on one toon, save that profile as "general configuration". Then you can copy that profile to your other characters and tweak it for them as needed under a new name (for example if you use VuhDo, you'll need to, of course, tweak what spells, hot icons, etc, shows on each of your healers).

If you are a raiding with multiple characters, another time saver is to make any raid-buff or raid-debuff power auras you use (if you use that addon) on the "global" pages rather than the "local" page. Then when you hop on an alt to run an alt raid or pug, you'll have the big GTFO or critical buff reminders already made. Similarly, for procs that are common between your characters, having one global power aura for them all can be nice (I mainly use this for Powertorrent and Landslide procs, for example). Rather than having to remember how you made the proc indicator on each toon, you have a unified look.