1. Every plane has a reference mark on one end or the other that shown the proper orientation of the plane to the surface of the board being cut.
2. By tapping the friction wedge lightly with a small hammer, one can usually keep the blade in position but it often moves. Don't over tighten, as you risk splitting the plane body.
3. Try and use tight grained clear pine for mouldings. Use quarter-sawn lumber if possible. The consistent grain and texture of the soft wood makes for easier planing.
4. Keep the plane's blade sharp and only have it's depth protrude just enough, so that the chips wont get stuck in it's throat opening.
5. Start slowly and try and run to plane the whole length of the board. Once the profile begins to be cut it will provide a reference for continued planning.
6. The depth of the profile is determined by a stop which is milled into the sole of the moulding plane. It makes it so that the plane simply wont cut past a fixed depth. This reference is usually parallel to the face of the board being planed.