I do begin lessons from the known to the unknown. I believe Relevant previous knowledge of students is vital if they are to understand any subject matter at hand. This is so because it helps them to relate what is to be learnt with something they might know already.

I really love to also review previous lessons to ensure they are properly grasped before moving on to the new lesson.
In areas where graphical presentations are needed to aid in understanding, I do not hesitate to provide same.

Finally I believe every learning experience is to be fun and enjoyed, thus there is always a few minutes in each lesson to heighten interests.
With over 5 years of teaching students with varied backgrounds and intellectual abilities, spotting short falls and their causes in comprehending the lesson is not a difficulty for me. I can easily see why a student is actually struggling to understand a particular point and thus break it down into systematic bits to follow and understand.