I could write a book on how to fake it. And this would be part of it...
In truth I spent WAY more time in preparing my clothes for each meeting then I did preparing for the lessons. So... (take notes)
I would skim a few days ahead and highlight lightly (not heavily per Billy's comment above LOL) ususally words before a scripture would work and a few things in the middle just for a visual sense of balance. THIS IS IMPORTANT - from a distance, people want to see overall coverage, heavy in one area and lax in another may be realistic, but it doesn't say "all around" - you want their eye to capture the visual of your "preparation" and move on. I didn't use highlighters too much myself. Historical references I would look up sometimes just to get ONE fact no one else knows and use it as a commenting point (WARNING - don't dive too much into history.... you do that, the entire JW structure begins to fail). I would then look for all scriptures that say “compare” or were referenced without quoting and write down the basics of the scripture in the margins. I would make LONG arrows that went across the page so everyone around me could see the notes I made. The written notes make more of an impression than highlightling... and it could be Marilyn Manson song lyrics for all they know, the fact is it looks like you are DENSE with study and information. Maybe 15 minutes per WT study (in this example) IF THAT.
The rest would be “on the fly” as the meeting was in progress by knowing how to work the system. You have to pay attention to the feel of the room and give the audience what they want. In some cases I would skip ahead for any gospel accounts and would quickly look them up to do a “context of the scripture” comment that always seemed to wow the audience (because it made it sound like you researched). In reality ALL the gospel accounts are of Jesus walking somewhere talking to someone... you just need to scan to remember who and where and somehow apply it.
Also pay attention when new people comment because sometimes they give SLIGHTLY off comments and if you are there for a follow-up comment to gently and non-offensively shave what they said into something more accurate, then it makes you look AWESOME as you saved the dignity of the new person while still maintaining the spiritual health of the congregation. There are always at least 3 people in a congregation that when called on, I stopped whatever I was doing three paragraphs ahead and listened to because I knew there was a strong possibility I would need to chime in with a clarification comment. The elders eat that shit up.
For annoying people, you can spend a few meetings paying attention to the KIND of comments they make. The more uptight they are, they more rigid their study pattern - they stick with what works because they stick with what IMPRESSES. You can pretty much predict the comments they are going to make. SO MAKE THEIR COMMENTS BEFORE THEY DO. It's tons of fun. They work SO HARD on like... 4 comments for the meeting. To deflate that just sit where you can see their magazine... and note whatever paragraph they have LOTS written on. You know HOW they comment. Skip ahead and get your hand up first. Enjoy.
I would be quiet the first quarter of the WT study (in example), to see how the group was feeling then comment lots, then quiet again (preparing), then comment lots toward the end. And I always wanted to comment a lot toward the end because that is what people remember... and they come up to you after the meeting to say how much they enjoyed your commenting.
There is a rhythm to the religion as a whole, you know. Once you notice the ebb and flow of it's cycle you can pretty much fake everything by custom fitting it to your particular congregation. I noticed after some years I had so much bible shit piled in my brain, I could pull stuff out extemporaneously without batting an eye just by altering it per the last convention or whatever.
Honestly though, once I learned how the flow of the congregation worked, I knew what kind of comments worked and what the people wanted to hear. Preperation just gets you the tools. HOW to use them properly depends on the collective energy of the group at the time. I just happened to have turned it into an artform. :-)