from a retired high school teacher...

when you make up your lesson plan, look at the lesson plan template from your local school district... the Scouts should be familiar with that form of presentation

about 45 minutes is all the lecture you should attempt without some form of a break
you might modify a "Frayer Diagram" (change the names on the quadrants) to organize your packets if you plan on any note taking from the Scouts

when you do your hands on, and if you use groups... one Scout will become the leader... don't let one do all the work, make sure everyone gets a chance to show their skill level

basic mantra.... tell them what you are going to tell them... tell them objective 1, tell them objective 2, tell them objective 3... tell them what you told them

make sure the rubric of what is necessary for award of the merit badge is understood to assure there is no misunderstanding (it's been a long time, and I only made it to Star, so don't know what the BSA uses)