Whats the CSS to make something go to the next line in the page?

There are two options that I can think of, but without more details, I can't be sure which is the better:

#elementId {
    display: block;
}

This will force the element to a 'new line' if it's not on the same line as a floated element.

#elementId {
     clear: both;
}

This will force the element to clear the floats, and move to a 'new line.'

In the case of the element being on the same line as another that has position of fixed or absolute nothing will, so far as I know, force a 'new line,' as those elements are removed from the document's normal flow.