This is #1 and always will be - no exceptions. Shower, shampoo and shave, even if you have a beard, on at least a daily basis and always before going out to socialize.
Every gentleman's top priorities are hair, nails, clean well-ironed clothes, and freshly polished shoes. Women love shoes - make them love yours!
The more things change the more they remain the same. Today's men's fashions are hybrids of haute couture of the early 20th century, when clothing was designed not just for look but also for purpose. There is nothing more enjoyable and better looking to wear than a classically designed, well-made, properly fitted suit. You won't likely find one off the rack, so do make friends with a bespoke tailor. (Bespoke means he does custom work from your measurements.)
If you wish to eat like a pig, try the swill at the trough! Otherwise: wait until everyone is seated and served before you tuck in, try not to talk with your mouth full, chew your food slowly and quietly, and use your napkin, not your sleeve. As for the classic "Which fork?" conundrum, the general rule is start with the one on the outside and work your way in with each course. Or do what your host is doing!
Even in these hectic times, practiced manners and a courteous attitude will always be in vogue. Little things like opening doors, seating your guest in her chair, showing interest in her conversation and concern for her well being, and following up dates with a thank-you call or card will endear you to her forever.