This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
The Salchow starts from an "open" LFO 3-turn followed by a strong
check on the LBI edge. Leaving your hip open will extend your free leg
behind you in the direction of travel. As the skating leg rises after
the check, the free leg and shoulders are released (swung around) and
the skater jumps, landing on a RBO edge after one rotation. If you go
back and look at the tracing you left as you took off, you should see
a pronounced curve, shallow coming out of the 3-turn, and deeper just
before takeoff with a toe pick mark at the end (like a check mark)
indicating that you were rotating forward on take off. In this
respect, a Salchow is not unlike a Waltz jump with a backward entry.
The Salchow is an incredibly easy jump to cheat, and the easiest way
to cheat is not to have or hold any check following the introductory
3-turn. Since cheating is bad, reduces power and control, and is hard
to unlearn, start out by learning the jump without the cheat.
First, practice the approach WITHOUT the jump. From a RBO edge, step
forward and turn a LFO 3. HOLD IT. HOLD IT. HOLD IT. Practice holding
the entry edge on the 3 turn, right leg extended back, body strongly
checked. This is the position that you want to have before the jump.
Practice this a lot, until you get familiar with what is involved in
holding the edge ... where your shoulders are, how open your free hip
is, where your free leg is, etc. A LOT of the power for the jump comes
from creating momentary rotational tension by initially checking the
rotation of the 3 turn.
Remember that virtually all of skating is done as a series of down up
down up down up down movements. The introductory 3-turn requires a
DOWN to prepare, an UP to turn the 3, a DOWN to finish the 3, an UP to
do the jump, and a DOWN to land it. Don't forget any of the "downs",
because if you don't go down there is nothing to come up from.
The Salchow has a 1, 2, and 3 cadence. 1 - turn, 2 -check, and - let
the free leg and arm move from behind to inside the circle, 3 - jump.
There are two primary sources of rotation: the edge you are on (should
be deep), and having the arm in back come forward during takeoff
(which rotates your shoulders). The jump comes when you progressively
deepen the back edge by releasing the free side, closing the free hip,
throwing/pulling the free leg forward and up, and by scooping your
arms in/down and up.