TO INTRODUCE THE FIRST OF TWO ACTIONS

BEFORE (c.) (f.c.) (p.)
      Wake me up before you go (c.)
      Enter the house, but before, you have to disconnect the alarm system (f.c.)
      Don’t just open the door. Before that, ask who is knocking (f.c.)
      I met Charles before lunch (p.)

WHEN (c.)
      When I opened the door, the dog looked at me and went out  (First I open the door, then, the dog goes out)
 
If we want to emphasise that the second actions happens immediately after the first one:
 
AS SOON AS (c.)
THE MOMENT (c.)
      Phone me as soon as you see her
      The moment I saw her, I lost control

TO INTRODUCE THE SECOND OF TWO ACTIONS

AFTER (c.) (p.)
       After the bomb exploded, everything was quiet
       I went out after work
 
AFTERWARDS (f.c.)
THEN (f.c.)
LATER (f.c.)

Later suggests an interval of time between both actions. Afterwards and then can be used when there is an interval of time or when the second action takes place immediately after the first one.

      There was an explosion. Afterwards/Then, everything was quiet
      She had a shower. Later/Afterwards/Then, she went for a walk

If we want to show that the second action happens quickly and unexpectedly we use:
 
SUDDENLY (f.c.)
      I saw her. Suddenly, I lost control

  TO INTRODUCE THE FIRST OF A SERIES OF ACTIONS (2 or more)

FIRST (f.c.) often used with "then" or also with "second", "third", etc.
      First, go into the house, then, go upstairs and wait for me
      First, switch it on. Second, search for the channel, and last, adjust the volume

abbreviations:  (c.)= conjunction   (f.c.)= free connector  (p.)= preposition    (see the important difference here: Kinds of Connectors)