I'll reiterate here about cleanliness, short fingernails, and clean shoes and scrubs. Those are important no matter what sex you are, or whether you're a student nurse or a full-fledged, ass-runnin' nursey type.
However, there are a few boy-specific tips I can share:
Tip The First: Beards: either don't have one or keep it neat.
I love a good beard. Really and truly, I do. However, something that's chest-length or scraggly or otherwise unkempt should either be shaved off or neatened up. Same goes for pornstaches of any description: if you can floss your teeth with it, it's too long.
And don't ever go with long sideburns or muttonchops. Please.
Tip The Second: Shaving: early and often.
Please, guys, shave before clinicals and/or coming to work. There are about a jillion ways to remove hair from your face and neck; if one doesn't work, another certainly will. Razor bumps can be kept at bay with a quick daily swipe of a Stridex pad. Trust me: I have more acreage to shave on a biweekly basis than you do, and Stridex works.
Tip The Third: Leave the bling at home.
Nobody wants to see masses of jewelry on women, and nobody wants to see it on men, either. A class ring plus a wedding band is all I really want to look at on your paws. The large crosses or eagles or whatever you're stringing around your neck should either be tucked under a shirt or taken off.
Tip The Fourth: Underwear. It matters.
Especially for those of you wearing whites as students (and thank God the schools I work with are getting away from them), undies matter. Print boxer shorts, blue briefs, or weirdly colored...er...mesh things will show. White underwear under your whites, please (do they sell men's underwear in nude/buff colors? I don't know), boxers or briefs or whatever. Don't make the mistake The Late Lamented Friend John made of wearing Valentine's boxers under whites.
Tip The Fifth: And this one is unisex, about piercings and tattoos...
Piercings and tattoos bother me not a bit. I should not, however, be able to see either easily while you're a student (restrictions relax a little at my facility once you're hired). Piercing shops sell nearly-invisible keepers for holes pretty much anywhere in your face. Tongue piercings are usually not an issue unless you're one of those annoying people that clacks it against your teeth constantly. Just make the effort. That's all I ask. (Note that if you wear a piercing or tattoo as a religious or cultural matter, you should not be required to take it off and I will back you up to the hilt on the matter.)
Tats are a little trickier to deal with. Covering them up is your only option. One of my dearest ex-coworkers, now in nursing school, has to wear UnderArmor under his whites on a daily basis, because he has two full sleeves. This will not affect his job prospects, I don't think, because Dr. Skippy has two full, gorgeously colored sleeves himself, and he's a damn surgeon.
(Oh, yeah: if you have noticeable nipple piercings, please put, I don't know, maybe a band-aid over them. Or wear an undershirt. That stuff can be really, really distracting.)
Tip The I've Lost Count: Hair other than that on your face.
If you have a luxurious growth of chest hair, bravo for you. Please wear a crew-necked T-shirt under your scrubs. I work with a surgeon who, despite being a mild-mannered type, is furred to an extent that I didn't think was possible, and I know more about his chest hair than I really want to. Ew. Don't make that mistake.
Likewise, if you have long hair--and this is particularly important for guys, as long hair is still seen in some parts of the world as a little daring--it *has got to be neat*. Ponytails or a single tight braid are more than acceptable. Again, if this is a religious or cultural requirement for you, there should be no question but that you're allowed to do your thing. If it's not, though, make the effort to keep that stuff under control. Shaun White's a damn cutie, but I wouldn't want him changing a sterile dressing on me.
Tip The Final, on Special Considerations (also unisex):
I've worked with Muslim women and Sikh men both as students and as coworkers. I've worked with Indian women who wear a bindi or a red mark near their hairline, Christians who veil or wear only skirts (the women, not the men), conservative Jewish men who have full beards, and even a couple of First Nations men who'd never cut their hair in their lives.
Whether you're wearing a nose ring, a bindi, a headscarf, or a turban, to do so is your right. If anybody gives you crap about it, you might have to go up the chain of command until the situation is resolved, but DO IT. Religious symbols worn on the body are a right, especially if they're an integral part of your beliefs, and you can work out a way to maintain that symbol without it being a distraction. Do not let anybody tell you different.
And, if you're working with me and somebody gives you shit about your cap, your bracelet, your unusual underwear, or your nose piercing, I reserve the right to beat them half to death with a used Foley catheter. Just come see me during normal business hours.