Let's say you already have crown and base:
1) Add molding in rectangular blocks on the wall. You can paint just the trim, or add color inside the blocks.
2) Try a chair rail. For 8' ceilings I recommend going as high as 42" from the floor. Most dining chairs have high backs and the standard 36" height may not look balanced. When you have 9' and taller ceilings, I use an element from the space to determine height - that can be a window, the light switches, cabinetry and more.
3) Wainscot creates a finished and elegant wall. Sometimes a very low wainscot works well, otherwise I go 40-46" from the floor.
If you have molding detail and crave more, create a grid on the ceiling for a statement look. For ceilings like vaulted and low basements, this can be a great place to hide wire to drop new light fixtures into the room.
The color of your trim should generally match existing doors and casings, BUT contract trim, tone on tone trim, and even a bold color will work as the space dictates.
If all of the above are too much work and expense, add pre-made ceiling medallions as architectural detail.