First was for college, the second one is for my part time job.
Most places don't have penis inspections anymore, but if you're unlucky enough to live where they still do them, there really isn't anything you can do to get ready for it.
The guy has you drop your pants, and usually checks your balls first for lumps and whatnot. He doesn't have to squeeze very hard to do this, but sometimes they do, just to be mean. Cold hands are also very common. He'll wear gloves, unless he's a fag.
Then a visual inspection of your penis, looking for lesions, warts, anything indicative of an STD. You'll probably be fine there, virginfag.
The worst part comes at the end, with the glass tube going up your urethra. I think they're using some kind of plastic now, which is much safer, but it still hurts like hell. Once he pulls it out and wipes a swab with it, you're done. They send the sample off somewhere and if you don't hear anything back within a week or so, you've passed.
Good luck, and remember not to cry. That really makes you look like a pussy.