I never understood how people use hotbars. I click hotbar buttons when swapping gear (trapping, haggle) or placing torches in challenges, but other than that I really don't use the hotbars much at all. Most everything I do is with keyboard hotkeys, leaving the hotbars to just show me cooldowns. And also to remind me what keys do what.
My "action" keys are the numeric keypad, plus the bank of keys with home/end/etc...
Then my hotbars mimic those relative positions similar to the following, which is for my challenge farmer monk:
When I want to cleave I hit 7, great cleave is 8, etc... My attack key is 4, so I put my combat stance (power attack or precision) on 4 since the attack key isn't mapped to a hotbar location. For melee I put weaponsets along the outside of the numpad, with alternate versions mapped to the Alt key:
For example, I could put my +++ greensteel undead beaters mapped to ".", and a set of crafted undead beaters with better dps but no insta-kill for undead bosses mapped to "Alt+." Those weaponset mappings (and their Alt versions) are assigned to Hotbar 6, which isn't visible since they're the same for all my melees.
I also assign the entire Alt alphabet (Alt+A, Alt+B, Alt+C, ..., Alt+Z) to hotbars 8 to 10, and then move common actions to the appropriate letter. Alt+C is remove Curse, Alt+T is Teleport scroll, etc... I don't need those to be visible because they're set to be obvious and easily remembered.
And finally, Hotbar 7 is my shrine buff hotbar, which I map to Alt versions of the home/end/etc... bank of keys, meaning I get up to six shrine buffs for any one character. When entering a quest or after shrining, I hold down Alt and just rapid-fire through that bank of keys until they stop responding, meaning I did them all. Doesn't matter what the actual shrine buffs are; I always use the same keys for all characters so I never have to worry about forgetting any.
EDIT: The third image is very old. The "1" key has been Unbalancing Strike for years. I haven't used Storm Strike since the enhancement pass in 2013. Also, in the second picture, all those weaponsets in the home/end bank of keys are from years ago when I used to have crafted boss beaters for various niche bosses: monstrous humanoids (gregor in crystal cove), demons (devashta in extraplanar palace), reptiles (that squirrely boss in rushmore mansion), etc... I've long since switched to just using my trash beaters (Scraps of Enlightenment) for just about everything except undead and the lantern archon in kobold island.