Take your lesson
Open a new window and load your page as a student would see it. Take the lesson yourself - it should be easy for you :) - and look for any rough edges. Are all the elements you wanted to introduce or explain properly introduced and explained? Do you feel like you introduce new material at a good pace? Does the lesson cover all the material you want? Also look for typos or missing punctuation. And, of course, fix anything that is incorrect, missing or not clear.