Despite the seeming omnipresence of "metrosexuality," the average straight male who finds himself intending to wed is, like most men, in need of at least a little constructive criticism on the subject of grooming. Never fear, though - after the nuptials, you can revert to a state of general cluelessness about your appearance!
Know this, however - your bride is expecting and needing you to look, smell, feel, sound and taste as good as you possibly can. This isn't going to be difficult, gents; follow me through this and we'll get it all done as painlessly as possible.
1) Hair: Don't do anything stupid. Consider, months in advance of your wedding, visiting a salon. (If there was ever an occasion to justify a $40 haircut, this is the one.) That being said, don't take any last minute gambles. Even if the haircut is an expensive one, don't go anywhere you haven't been before, and don't use a stylist you don't trust - it's not worth the risk. Do attempt to have you hair freshly cut before the big day; this will put a damper on split ends and uneven lengths.
As far as general care goes, consider developing a regime of using conditioners as well as your normal shampoo a few weeks prior to the event. If you have dandruff, pay special attention to finding a solution for that. You don't need a winter wonderland on the shoulders of your tux.
2) Skin: If you have any problems with your skin (acne, ingrown hairs) that could be easily dealt with, deal with them - see a dermatologist about acne control, for example. If your beard is prone to ingrown hairs, try only shaving gently with the grain of your follicles, and use a single-bladed razor. You won't get as close of a shave, but you also won't have a face full of angrily impacted pores, either.
Ask a female in your life about facial powder - stage actors use this stuff to keep their faces from looking like beacons. It soaks up excess facial oil or other moisture, and it'll really help your skin look natural during photographs. It's not "un-manly," either - it isn't going to change the tone of your skin or make you look like you have makeup on.
3) Mouth: Your mouth is most likely the part of your body that could stand the most improvement (as far as health and appearance) at any given time. If you haven't been to the dentist for a cleaning in
then what are you waiting for? While you're there, talk to the doc about any whitening procedures he could recommend. It never hurts to get the pearly whites a little whiter than they are at the moment.
4) General stuff: Cut your fingernails. You don't have to get a manicure or anything, just cut them so they aren't ragged or long; there's no need to scratch your bride as you put the ring on her finger. Don't forget your anti-perspirant/deodorant combo that you wear every single day (right?). Use a dash of cologne that you know she likes. Bring along a few mints for the reception - you're going to be in very close contact with a lot of people, so you don't wish to offend anybody with your breath.
Keeping on top of all this stuff can be a pain, but it's worth the trouble - your bride will be pleased that you took the time and effort to make yourself as attractive as possible. This satisfaction with your efforts could pay off in lots of exciting ways