I notice whether it is a disaster zone, or relatively neat (and I'm very good at guessing whether it was one of those "omg! Girl coming over" try to shove things out of sight or more of a lifestyle. I guess my goal is to have an idea whether I actually want to know whether his standards are about the same as mine - it will make both of us more comfortable in each others places, if we are.
Secondly, I notice the style/decorative items/anything that gives hints about his lifestyle/sport interests/past/family photos etc. Goal for that is probably just getting to know him better and (well maybe not the first time, but eventually) help me know what sort of things he might find cool or could use in his apt in case I ever need to buy presents down the line.
Style. If it's too stylish, either he's too materialistic or closet gay.
Smell. If it reeks of air freshener or is stinky, I won't be there long. If it has a clean smell (not over-the-top), I know he maintains his home.
Bathroom. The ladies below said it well.
Kitchen. A clean sink/stove/fridge means he knows how to maintain the kitchen. You can also tell if he knows his way around the kitchen by the items IN the kitchen. If it's a Spartan kitchen, I'll know he doesn't know how to take care of himself and ends up eating out all of the time.
As long as the house isn't piled up with crap, I'll know he tries. I don't expect a sterile operating room. My house is far from that. Dust can accumulate within two days, so that's not a big deal to me either. Just make sure I won't get some funky bacteria/virus if I eat at your place. That's the bottom line really.
I look for the comfort level at his place and how much it represents him. I'd rather prefer his place to be NOT a clean freak material. A bit messy here and there yet clean where need be. But, then again. I don't want the place to be dirty and messy everywhere, that would contradict the comfortable aspect. A comfy couch is the main thing I look for when it comes to comfyness.
I also look for how well his place represent him. If he loves to read. I'd expect a collection of books and if he loves music in general. I'd expect to see various records/cd's and if he's a gamer. I'd expect to see XBOX and guitar hero lol
In general. His place should be comfy and should represent him.
Lol I make sure there aren't pics of a girlfriend / wife. See how well he can coordinate, decorate, and accessorize. Of course I see how clean and organized he is and just to make sure he didn't just straighten up the house because a girl was coming over, I check the bathroom. For some reason if a messy guy is only cleaning to impress, they always overlook the bathroom lol.
I mostly look for signs of downright grossness and lack of basic hygiene. Of course, the bathroom (not just the area around the toilet, but also the sink and the tub or shower). There's also the kitchen, especially the food stored in the refrigerator. And maybe a closet or drawer or two. If the place passes the "eeww" test, then maybe I sneak a peek at his books and his videos and his music.
Ok, I am a compulsive cleaner and neat freak, borderline OCD. BUT I do realize that there is a difference between men and women and cleaning. But for the most part, I notice if he sleeps in his bed with all of his clothes and I really notice the bathroom and kitchen area. Those areas should be clean and tidy.
I believe your home should reflect you. If I don't feel comfortable enough to sit down, I probably won't be coming back for a visit.
When I go to a guys place for the first time, I expect it to be comfy. Not to organized but it looks like someone actually lives there. My house isn't all that organized. I have my homework in a huge pile on my table in the kitchen. As long as the house doesn't look a mess and it's tidy enough to walk on the floor without stepping on anything, I think it's ok. [and I don't think dusting is in order unless your house hasn't been dusted in forever. ]