Ralph Lauren has been in business for quite some time (since 1967 to be exact), and has become one of the best known American fashion designers of all time. I'd say that's enough experience and credibility to know a thing or two about style rules that men should follow. Anyway, Ralph Lauren put up a series of menswear rules that I think are fairly spot on. Wanted to put them up here and give a bit of my commentary in case you're interested. Here's the first three:
I know why this is #1 in the series. In my opinion, it's the most important. Fit is indeed everything, and people can tell.
Before anyone knows the brand, the fabric quality, or whatever, they can immediately tell if something fits well on your or doesn't. This is why it is important for you to buy the right sizes, find designers that fit you well, and get things tailored if they don't fit you well off the rack. A shirt that is 2 inches too long, or a jacket that has slightly large shoulders can really make the difference between you looking mediocre, and looking glorious (or exquisite, fantastic, amazing, simplerman-ish hah, etc.).
I know there are a lot of things you need to keep in mind when finding the right fit, but just to give you the rundown, you need to pay attention to: body/pant length, body/pant width, collar size, shoulder seams, sleeve length, armhole size, waist size, and rise, among others. Don't compromise, and use tailors liberally. Again, remember it's #1.
This rule is one I agree with as well, but only to a certain extent. Yes, if you unbutton one of your shirt buttons, it is customary to take off your tie as well. However, to me, this is not a steadfast rule by any means, mainly because unbuttoned collars with loose ties can look great on the right occasions.
Do I propose you loosen your tie at a business meeting? Probably not. However, let's say you just left a dinner party that you suited up for earlier, and are ready to dance it up at the night club. Loosening that tie may be the best look for you, as it gives off the image that you were at something important before, but now you're ready to relax and have some fun.
When buying a tie, it's important to write down or remember the width of your suit lapels. When someone wears thick peak lapels with a skinny tie, it just looks off. Likewise, wide ties don't look very good on jackets with thin lapels. Now, the rule is that the widest part of your tie should be directly proportionate to the widest part of your lapels, but I say there's some wiggle room there. No man will randomly come up to you to inspect your tie's exact width against your lapel's exact width. Frankly, that would be ridiculous, and I would probably shove that dude away for coming so close to me.
Instead, ballpark it and don't worry if the tie doesn't exactly match up to your lapel. Just make sure that you know which ties go with which suits in your collection, since it does actually matter what tie goes with what suit.
Anyhow, hope that helps some of you out! I'll bring you some more of these, but thought it would be good to start somewhere.