Can't remember where I found this, but here are some good pointers...
Here are my suggestions for getting a jumpseat and appropriate jumpseat ettiquette:
1) Travel in uniform. It always helps identify you as a pilot and often clears some of the bureaucracy. If you're not traveling in uniform, you'd better be traveling in business class attire (slacks/collared shirt), and have a tie available in your suitcase just in case- some places still have tie policies on the books and some captains might hold you to them.
2) Try to catch the crew at the gate when they come up. If that's not possible, ask the gate agent if it's okay to pre-board so that you don't interrupt the closing of the flight or get in the way of boarding passengers.
3) If you can't pre-board or meet the crew at the counter, when you go down the jetbridge, leave your bags at the door to the aircraft, off to the side and out of the way of boarding passengers. Enter the aircraft and politely introduce yourself to the lead FA. " Hi! My name is Bob, I work with XYZAirlines and am trying to jumpseat today. Mind if I poke my head upfront?"
4) Once you get the go ahead from the FA, step up to the cockpit entry way. Double check that you have EVERYTHING THAT YOU NEED TO JUMPSEAT READY. You should have your medical, certificate, boarding pass, and company ID all set to hand to the captain. If you're flying via the CASS system, you should also have your passport out and ready.
Odds are the crew is doing something. If they are running a prestart checklist, WAIT UNTIL THEY ARE DONE WITH IT! If they aren't running a checklist, knock on the cockpit door, extend your hand (to shake) and say "Hello gentlemen" or "Hello, sir/ma'am/captain" "I'm Bob Hoover, and I was wondering if I could ride along with you today."
Most captains at this point will do the once over- some might reach for scab lists or ask for additional verification of some details. If it's not 30 seconds to departure, there's nothing wrong with asking about the latest news at the company or some other mundane detail. If it is getting towards pushtime, thank the crew for the ride, offer your assistance should it be needed and hightail it out of there.
If you need to retrieve your bag from the jetbridge, stand patiently by the exit to the cockpit/galley for a break in the passengers. Most good FA's will ask the boarding passengers to wait for just a second. If they don't you can turn to face the entry and take a step forward (which 99% of the time will cause the passengers to stop), but don't try to push your way out. Also bear in mind that for this particular moment, the people boarding the plane might think that you're one of the pilots, so put on a smile and return any greetings that you get. Inform the lead FA of whatever seat you're in and let them know that they can call upon you if they need you in any manner.
Finally, once you get settled in and the flight gets underway, take a few minutes to WATCH the safety briefing. It's professional courtesy to the flight attendants. Don't put on your ipod or go right to sleep, take the 90 seconds to maintain eye contact and set an example for the rest of the passengers. You'd be surprised how much they appreciate it.
Last step is when you depart. If possible wait for most of the passengers to leave, unless you're in a hurry to connect or meet a showtime. Cross the seatbelts in your row- leave any trash on the seat cushion (unless it will spill), and then work your way to the front. Thank the cabin and flight crew for the ride and be sure to offer your company's jumpseat to them in return.
I followed this policy for 4 years of commercial flying and was never denied a jumpseat due to my behavior, and never had any uncomfortable moments like posted above. Most times I ended up in first class, although I think those days are pretty much over for non-revs with the number of free upgrades that they give out these days...
Have fun- Fly safe!