Things I like:
Module as a whole:
a) Lengthy "What has happened so far" description set out as a narrative explaining how we got to this point and what the major fronts that the PCs will be engaged with want and are doing absent PC intervention.
b) A good "hook" section that sets the stage for the PCs entering into the story.
c) Physical representations of any clues or documents that the PCs are likely to recover so that they can study them at leisure and add them to their notes.
d) Good imaginative maps of the major locations.
e) Highly Mobile NPCs or factions who might proactively move about should have their own detailed entries. This can require a list of "front" descriptions after the introduction but before the description of individual encounters. If for example the town guard might take an interest, "Town Guard" gets a front description along with a few named NPCs and some generic stat blocks to generate encounters from.
f) If there is a plot or expected flow of events, discussion of what happens if things don't go as expected. Adventures that just assume the PC's behavior, or worse assume the PC's will do something that is actually probably irrational are bad adventures. Adventures that have hard rails in place to get the PC's back on track rather than assuming a series of events that give the PCs a rational choice to get back on track are also bad adventures. Don't have things like, "The players will soon realize that they are vastly overmatched and run away, and then..." No, deal with the fact that players rarely act that way.
g) There should be a twist. At some point in the adventure, the players perception of events and what the adventure is should change. There are dozens of possible twists, some hard and some soft, but the twist should be there.
Individual encounters, whether events or location based:
a) Stat blocks in the description, not in an appendix. I hate flipping back and forth.
b) Things that are immediately obvious to the PCs set out first in a nice short readable block preferably set apart from the rest of the text. I find that if I have to improvise a description all too often I forget some important detail. I can always adapt the text if I don't want to just read it, but it should make good reading if I just want to read it.
c) Immediate things that are likely to happen set right after the intro block.
d) Points of interest based on things the PCs might explore set out as a list afterwards.
Depending on how complex the adventure is, it may need other support, but that's generally what I like.