I mainly use published adventures so I don't have to come up with everything myself. I am not that kind of creative.
Running a published adventure, I basically have two ways of running it:
a) as written.
b) de-constructed and remade.
Option a) is obviously the least work. It generally isn't too fun, neither as a DM or a player. Most of all because most adventures are kinda rail-roady. Option b) takes a bit more time, but not necessarily so much more. Let's take a typical part of a published adventure: a medium sized dungeon. Usually it's divided into encounters which has certain assumptions about what the PC's have done and how they enter the room. What I do is just make a list of all the monsters, by room. It's easier if you can make a quick copy of the dungeon map and write the info on the map, so it's more visual. Then I read through the encounters, making short notes on each "encounter" or important NPC. After this, I am ready to run the dungeon. Now I have the information to run a much less static dungeon. It's easier to "kill" some monsters in a room - if they joined a fight in another room, or move monsters around as the situation changes. An attack and then a retreat from the PC's may change the monster distribution completely.
Running the Starer Set module I changed how the castle behaved, after the PC's attacked and then retreated. I sent some of the monsters with bows outside, on top of the roof of the castle to more easily spot intruders and to more easily overwhelm the PC's. They could then alert the monsters inside and attack them from inside the castle. Nothing of the kind was written in the module, but after de-constructing the castle site, it made complete sense (to me at least).
This is one of the reasons I think that adventures could have been written in a much more condensed format, something closer to my de-constructed format. A map with the monsters and their "normal" location (written on the map). Some short notes. A more detailed description of the different rooms and the NPC's and their behaviour and plans. Much more useful than having to flip through 7-8 pages to get a full overview of the same dungeon as it typically is now.
I ran Reavers of Harkenworld using the above approach (actually my first time trying it out) and I think it worked really well. It felt more like one of my own adventures, but with much less work - mainly because I didn't have to find the monsters, create the NPC's and come up with a plot. I just had to de-construct the adventure (reading through it, taking notes on the relevant map), and when running the module mostly rely on my notes and the premade monster stats. Since my preparations didn't rely on the PC's doing as the adventure had assumed, I was much more open to the players wacky ideas and just running with it without having them running into glass walls like in crpg's, which is very easy to do if I hadn't prepared for a more open game style.