I did a quick search on this board to see if I could find a post that explained a bit more about using id's and classes. I am trying to figure out where it is appropriate to use one or the other.

From what I have read and seen would it be correct to say:
Use ID's for main blocks of content or blocks of text (ie just in the DIV/SPAN tag)
Use Classes for individual HTML tags such as images and also for formating text

It's just because when I begin to design my new site (which I am trying to leave tables behind in) I want to know how to best set up the css.

Thank you.