How so?
I threw in the cigarette smell as something they could look into further if they wanted to. There's no expectation that they will; indeed it's quite possible the smoke-smell piece will get overlooked or unheard in the rest of the description, and that's fine too. But if they do want to do anything with that element, it's there and they've been made aware of it.
You earlier indicated I should only describe the man (and the flies) as he's what the players/PCs are most likely to want to interact with and could well be the reason they are there at all. What that does is point them directly at the man and in effect makes everything else in or about the room irrelevant.
What I want to do instead is give them multiple elements - the man, the window, the hole in the wall, the smoke, the bottles, etc. - and let them choose which to interact with; and even though it's still highly likely they'll beeline to the man and mostly ignore everything else, they have other options. Also, if it turns out that any of those other elements happens to be relevant now or later e.g. there's someone listening on the other side of the hole or beneath the open window, they can't later say I never mentioned that element.
You say "makes everything else in the room irrelevant". But why would that be? I mean, suppose I describe the room as per my first alternative above:
You open the door, into a poorly furnished office. There's a man sitting, slumped, in the simple wooden chair. Flies are hovering about and above him. You can't see his face. He looks like he's dead.
A player might ask "What do I smell?" Whatever the answer given, we now have something potentially relevant. Or might ask "Is the window open?" Now the window is relevant. Or might state "I go to the window! What do I see?" Again, now the window is relevant.
A crisper description doesn't preclude the players asking questions, any more than you description does. And we've already established that your description nevertheless
requires questions, in the sense that the players must ask questions to learn about the flies, or the absence of butts in the bottles, or the presence of bottle caps.
What your description
does do is make something salient
other than the question of the identify of the man, and his status as alive or dead - namely, the hole in the wall, the smell of smoke, etc. This is where the tension lies - you say that you do not want to create expectations or lead the players, but in fact you are doing exactly those things, by choosing to foreground certain facts that - from the players' point of view - were hitherto not of significance to them.
If you, or any other GM, wants to introduce "hooks" into the fiction to try and catch the players' interest, well that's your prerogative. But it seems odd to deny that that's what you're doing!
Going further, if one isn't supposed to critique GMing techniques unless they have GM'd, does that give a lot of cover fire to folks suspected of being railroad conductors? And a free pass to those DMs who are in situation of being the only DM around?
Before one gets to the stage of
critiquing GMing techniques, there's the stage of
identifying them.
For instance,
@Lanefan takes himself to be
seeding a mystery by not mentioning smoking paraphernalia in the context of his smell of cigarette smoke; but takes himself also to not be doing the same when he fails to mention the caps to the empty bottles, and fails to mention the flies, and fails to mention the open window.
As a GMing technique, how does this work? It requires the players to have some intuition as to what the GM regards as going without saying (and hence not worth following up on - flies, bottle caps) and what the GM regards as saliently absent (and hence worth following up on - smoking paraphernalia). It also requires the players to have the patience and inclination to ask questions that are
not connected to action declarations for their PCs. As in, "Do I see any flies?" "Is there an ashtray, or any butts in the empty bottles?" etc. Which are things that the PC would already by able to see, but which the GM has not bothered to describe first go around.
It mixes hooks to "sub-mysteries" in among mere colour. As
@Crimson Longinus has posted not far upthread, this in turn risks turning play into a wandering around looking for the hidden action.
That game is certainly not going to have the pace or the pressure of a gumshoe story, despite being - ostensibly - a "gumshoe game".
Have you ever GMed a RPG? curious
Yes, several. I linked you to an account of a session of Wuthering Heights that I GMed. I take it that you didn't click on the link.