How do I make a "leitmotif" or theme song?

[Johnny T]

Just looking for help or suggestions in creating a theme song, or "leitmotif" if any are familiar with the term. I guess I might just be asking "What () gives what feel?" Where () could be:
Key/Time Signature
Accidentals/Tempo
Notes/Chords
Harmony/Melody
Clef/Instrument
Chord Progressions
Techniques of any sort
etc.

I know "Major gives a Happy feel; Minor gives a Sad feel" and things, but what if it was supposed to feel scary?, evil?, heroic?, mysterious?, sorrowful?

Anything you can tell me would be a great help, and MUCH appreciated! Thanks in advance.  

[A B Up Start]

really just mess around with different melodies, chord progressions and tempos. like, i know what you mean, but i really cant describe in words how to get different feels.  

[Johnny T]

Well thanks for trying. I like to mess around, but I wouldn't even know where to start. Once I have a starting point, it'll be easy I suppose. I believe knowing what Key signature gives what kind of feel would be a good start, but I don't think it's that simple.  

[A B Up Start]

i got a nice creepy tune with the notes C G C# E#, C G C# F#

i used those with long notes in
http://8bitcollective.com/music/A,+B,+Up,+Start!/Ghost+In+The+Television/

and short notes in
http://8bitcollective.com/music/A,+B,+Up,+Start!/Ghost+Of+The+Windmill/

take a look at my other stuff if you want. my tunes tend to be mostly upbeat  

[Johnny T]

It occurred to me it might help if I specified I'm looking to make a leitmotif, but I don't know if any of you know what that means. Once more I appreciate anything to further my works to its goal.