For best results, rewrite the sentence as you think about how you’d diagram it, then diagram it. Rewriting seems like a waste of time, I know, but it allows you to purposefully write sentences and think about their parts. When you go to write your own sentences, you will have had practice thinking about what sorts of words you are writing, and this will allow you to understand the punctuation you might need to use.
Note: The following sentences use adjectives, direct objects, AND the motherfucking motherfucker. Click the sentence to see the diagram.