sirensong's book of etiquette, chapter 6:

opening and holding a door--

2 persons, walking in tandem, arrive at a door.  if said door is to be opened by pushing, the first to arrive shall open the door, enter or exit completely, and hold the door open for the following person.  the means of holding the door shall be to grasp the knob, bar, or edge of the door, instead of standing in front of the door, as the latter would reduce the space available to the follower as he/she passes through the doorway.  once the following person has completely passed, the door-holder falls back into tandem in the trail position.

if the door is to be opened by pulling, the leader shall open the door, hold it by the knob, bar, or edge, and step back, remaining on the same side as the follower.  once the follower has passed through the door, the door-holder passes through and falls back into tandem.

a side-by-side arrangement is somewhat more difficult to maneuver through, especially if one of the party does not know that the door will be opened/held for him/her.  in any side-by-side situation, the resolute student of graciousness shall act as though he were the lead dancer in a waltz, and gently guide the neophyte through the intracacies of this form of social gentility.

when approaching the door, the first assesment the lead must make is the particulars of the door:  primo, is the door to be pushed or pulled, and secundo, upon which side the hinges are located.

in any case, the object of the lead is to maneuver to be on the "hinge-side" of the door in question.  as all doors arc towards their hinges, this technique will prevent the lead from ungallantly "crossing the face" of the object of his esteem.  therefore, if the hinges are located upon the left side of the door, the scrupulous gentleman will position himself on the left of the pair by gliding around and behind the "follower" just before reaching the door.  

once the door is reached, use the same procedure as the "tandem" examples given above.  this will prevent what is commonly referred to as "the door dance", which is a frightful and embarrassing episode that is repeated ad nauseum is our grossly uncultured society.

while some consider this type of exercise to be obsolete, if not downright archaic, use of these simple guidelines will cause the practitioner to be esteemed in the highest and most mannered of circles.

Quoted: Quoted: Common courtesy in Texas for men that are total strangers to hold the door for each other. The only thank you exchanged is the man nod. An armed society is a polite society. I had a girl rant to me once about how she hated the man nod, felt that if they didn't want to take the time to actually wave to you they didn't really care about you.  I tried to explain, but she just didn't understand....

Those are the same women who, instead of saying "hi", always have to ask, "How are you doing?"

I want to say, Just fine since fifteen minutes ago when you asked me the same question.

I find it kind of amazing how blown away most women are when a stranger will open the door and hold it open for them to go through.  I always get a very nice, "Thank you" from them.  I guess chivalry is dying.  I think it's just good manners to hold a door for a lady.

Somone mentioned the "man nod".  Common courtesy too.  Hold the door until the guy behind you reaches the door.