Grid systems are one of the most useful tools in graphic design. They can range from a simple baseline grid and margins to a complicated modular system. Some examples:
I'm interested in how to decide on a grid system to use.
Do I need 3 columns, 7 columns, 12 columns, how do I know?
The baseline grid obviously has to relate to the font sizes used, so do I choose font sizes first then work out a baseline from there and work out margins, gutters and columns from that, or do I work out font sizes and baseline from the grid?
Where do I start?
Note: I'm specifically interested in print design. Grids in web design have a lot more technical limitations so lets stick to print.
When we had typography course and would design layout for a magazine, our teacher encouraged us to first take the content, analyse it, build an approximate grid that would suit the content best (only margins and columns, not baseline grid). Then try out different sizes that would work for the grid and give maximum legibility. If you work with printed material, the best way to go here is to set the text in different sizes and print it out. When you have chosen the right size for the font, you can set the baseline grid. Hope this helps!