Well, overexpose and underdevelop comes to mind! That is the same as B&W systems.
Adding contrast reducing materials to the developer is another. Add Sulfite to the developer (about 0.25 - 0.5 g/L) will lower dmax and/or contrast. Citrazinic acid in Kodak literature will reduce contrast in color materials.
Going up is another thing. Add peroxide to the developer, about 10 ml/L or underexpose and overdevelop.
Changing the pH is always useful. Up in pH raises contrast, but down in pH lowers it.
Just beware that all of these change color balance.
Be creative, try some things. That is the way to learn.