Smile, Dammit

• Smile, and be polite. Clerks deal with angry, frustrated people all day. They aren't required to help you they are just required to do the minimum. Maybe they will do the minimum for you anyway but it can't but help to smile and be polite.
• The boxes must be filled. Give the clerk many options; they have empty boxes so give them every reason to fill them in. I brought a signed letter from my employer [me] attesting to my intent to travel (which ultimately I didn't have to use).

Regular Passport (plus a little)

• Make an appointment at your nearest regional passport office. Boston has one so I assume every city does. The appointment system is an automated phone thing and they are overstaffed so you can make one during your drive/cab there. Bring your bags so you can go straight to the airport from the passport office. Keep in mind it is a federal building so you have to pass through a metal detector, etc [actual quote "Jimmy, stop screwing around and scan the bag. This guy wants to be someplace else."]
• Bring a printed itinerary of your impending flight. It must be within the next 48 hours and it can't be the one you just missed. A letter from your employer theoretically works but I didn't have a chance to try it. If you are smiling (see above) and show the gal the printed itinerary of the flight you missed she might suggest that the box must be filled but any valid flight number will do. Not that it happened to me, I'm just saying.
• Normal identification documents. Drivers license, birth certificate, etc. I had an old expired passport that they really seemed to like. The picture could have been any teenager, but they still favored it.
• Know your parent's birthdays. There are boxes for these on the paperwork and the boxes must be filled.

You may also spend some extra time in customs once you travel. The nice lady in Birmingham found it suspicious that my passport had been issued less than 12 hours previous. I pointed out that I was still wearing the same shirt as in the photo. I was "randomly selected" for extra screening on my way out of the UK by a Dutch guy. He quickly figured out I was mostly harmless but apparently had a time quota to fill so we burned 10 minutes talking about random things. He noticed I was from Pennsylvania and asked me if I was Pennsylvania-Dutch [I am] and if I knew "Dutch" had nothing to do with Dutch [I did]. He then asserted that the US term "dollar" was stolen from the Dutch. I counter asserted that it was from the ancient Greek thaler. I was definitely wrong (it turns out "thaler" is neither Greek nor ancient) but I don't know if he was right.

So when in doubt, smile and be polite. It pays great dividends and is a generally unremarked American strength. When I was in Lithuania a couple months back a girl said "I know you are an American because you are smiling" and as an American cultural attache I have to say that smiling worked out for me.