This is my current core hotbar layout:
https://i.imgur.com/xrRw8AI.png
I built it around a few core principles that work well for me:
Avoid using numbers above 4 or 5 for anything that you have to hit quickly
Bind core rotation and oGCD interrupt skills as much as possible to mouse buttons and the letters surrounding the movement keys (ESDF for me)
A few caveats about my setup:
I have a physical middle mouse button; hitting MMB is one of the quickest, easiest things for me to do, hence why my primary spammed GCD skill is on it. If your MMB is on your scroll wheel, you may want to pick something else.
As mentioned I use ESDF rather than WASD for movement. This layout would work just as well for WASD, you'd just be binding something other than W.
Finally, the bard in this screenshot is still low-mid-level. I'm familiar with the higher-level abilities and rotations, and I've tried to build my layout in a way that future-proofs it for them. Some things will move around once I get access to e.g. Perfect Pitch, but the principles above are generalized to be applicable to any character of any class.
