The ring menu does not bother me that much, but I really don't want to use it for spells I use all the time.

From the manual - "The Hotkey Bar makes even the tough life in blackguards a bit easier. Just open the Ring Menu and drag your favorite spells and abilities to the bar. Now you can activate those actions via shortcuts (1-10, E, Q) or clicking the corresponding icon. Keep in mind that every character has an own Hotkey Bar."

I tried that, it did not work. What element can I drag?

For spells you have to pull the little number, where you have to choose the spell level you want to cast from the ring menu into the ring of the hotkey bar.
For maneuvers and items you have to pull the icon of the specific maneuver you want to use from the ring menu.
Unfortunately you can't assign any 'menu'-ring to a hotkey, it's always the last step of interaction done in the ring menu, that goes to the hotkey bar.

(i.e. if you use a spell from the hotkey bar it already has its spell level fixed and all you have to do is select the target.
Assigning hotkeys is a bit of a chore, but once they're set it works quite nicely and really speeds up the battles.)

I managed to do it now.

It seems you can only drag it when you click very close to the center of the pie slice. That is a little strange.