Grid systems like the 960 grid and BluePrint can be useful to place the main elements for a website in a mockup: header, slider, content blocks, sidebar, footer etc. But do you use the same grid system to place the content within each of these elements?

I find that often quite difficult. For example I have a sidebar covering 3 columns for a table of 5 columns. I could actually create a mini-grid for the sidebar only.

I haven´t found a resource that answers this question specifically, so I´m curious to hear how you do this and if there are any "best practices" I´m not aware of. 

Cheers!