You end up with diagrams that look like this:
I found a useful tool that will draw these for your automatically, and it generally does a remarkably good job. Unfortunately, when it doesn't, or if you simply don't like the way it parses your sentence, there's no easy method for changing things, so you've either got to do some clever image editing or you're back to the start.
Modern linguists generally don't use Reed-Kellogg diagrams, preferring syntax trees, which look like this:
nice tool for these, which is generally quite flexible. It even lets you do subscripts like this:
More on sentence diagramming from Dave Barry: "Ask Mr Language Person":
Q: Please explain how to diagram a sentence.
A: First spread the sentence out on a clean, flat surface, such as an ironing board. Then, using a sharp pencil or X-Acto knife, locate the "predicate," which indicates where the action has taken place and is usually located directly behind the gills. For example, in the sentence: "LaMont never would of bit a forest ranger," the action probably took place in a forest. Thus your diagram would be shaped like a little tree with branches sticking out of it to indicate the locations of the various particles of speech such as your gerunds, proverbs, adjutants, etc.
Q: I don't have an ironing board.
A: Well then forget it.