What is Tone? 

The "mood" of the piece

What is Diction? 

The kinds of words the author chooses

What is Style? 

The structure/syntax of the sentences

Questions to ask regarding language:

Style:

1. What sort of sentence structure does the author use?  Are the sentences long or short?  Are they simple, or do they contain many clauses?
2. Does the author break any grammatical rules?  Why?
3. What kinds of rhetorical devices does the author use?  Why?
4. What parts of speech does the author favor?  Does the author use a lot of adjectives?  Action verbs?  Passive voice?  Abstract nouns?  Indefinite pronouns?
5. Is it easy to understand or hard?

Diction:

1. What sort of vocabulary does the author use?

2. What kinds of specialized language/jargon/slang/colloquialism does this author use? 

3. How does the author’s word choice reflect the purpose of the passage? 

Tone:

1. What sort of mood does the narrator (or author) seem to be in?

2. What values does the author assume he/she shares with his/her readers?

3. Is the text geared towards particular ages?  Genders?  Social classes?

4. How would you characterize the relationship the author sets up between him/herself and the readers?

5. What specific aspects of the text are obviously geared towards appealing to the audience and its values?