So how do you approach a celebrity to ask for an autograph?   Etiquette here is very important.  Remember to respect the celebrity's privacy, and to treat them with dignity and respect. Here are some tips which will make the encounter an enjoyable occasion for both of you.

1.  Always allow the actor his privacy.
    Never approach him while he is conducting personal business,
    i.e., dinning in a restaurant, shopping (particularly if he is with
    his family), at the movies or theater as part of the audience
    (see #2 - Movie Premieres and Theater) or in a house of worship.
    If you see him at any of these places, enjoy the memory of the
    sighting and the fact you did not cause him any undue stress or
    embarrassment.

2.  Places where it's acceptable to approach your favorite actor.
    a) Movie premieres - actually you can't "approach" him at a movie
        premiere, but you can stand in the designated fan area and
        wait for him to come over to shake hands and sign autographs.
    b) After Theater performances - depending on the theater and the
        actor, you may be able to obtain an autograph after the play.
        Check with the box office the night of the performance to see
        if this will be possible.
    c) Publicity Appearances - actors make different kinds of
        appearances for public relations and publicity.   Normally these
        are things such as charity events, autograph-signing sessions,
        film promotions, etc. Find out who the person in charge of the
        event is, and ask what the protocol will be for obtaining an
        autograph.

3.  Tips on how to make a good impression if/when you meet your
      favorite actor.
     a) Very important - don't shout.  It's human nature to shout or talk
         loudly when you are excited, but do your best to refrain
         yourself.
     b) Be nice and genuine.  Address him as Mr. Scott, not as Dougray.
         No matter how many times you've seen him in films, you do not
         personally know him, so do not be overly familiar.
     c) If you are requesting an autograph, have a pen (that works) and
         something that he can write upon.   Do not expect him to
         produce these items for you.  If possible, make sure that the
         pen will write properly on the paper or photograph you wish him
         to sign.  Test it first.
     d) Don't ask him to autograph a stack of paper or photographs.
         Limit your request to one or two.   He will want to accommodate
         others who are waiting, so don't monopolize him nor put him in
         an embarrassing situation.

4.  Some final notes.
     If you happen to be walking down the street (or wherever) and you
     see your favorite actor, feel free to smile and say "Hi", but do not
     stop him.  If he pauses to acknowledge your greeting, then (and
     you're going to have to read his body language very well!) it may
     be acceptable to stop and say something simple and genuine, such
     as, "I really enjoyed your performance in Ever After.   It made me
     believe in romance all over again", or something along those lines.
     Avoid gushing comments such as, "My god, you were great in Ever
     After! I just loved the gypsy camp scene where you kiss Drew!"
     You get the idea.  :-)