Some helpful bench marks from Colin Adams.
1. Reading or quoting from the biblical passage to be expounded.
2. Giving the basic thrust of that passage’s message.
3. Positively demonstrating the meaning of the text by supplying relevant supporting evidence to your interpretation (historical background, literary context, grammatical support, word studies, wider Scriptural cross-reference, etc)
4. Negatively clarifying what the passage does not mean; ruling out possible faulty interpretations.
5. Drawing out the lessons of the passage for believer and non-believer.
6. Relating the passage to Christ and his gospel (setting the text within the wider framework of biblical theology).
(Note: non essentials to exposition include catchy introductions or conclusions, illustrations, numbered points, alliteration. No doubt some of these can be helpful on ocassion, but you could do exposition without them).