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[Stanley]

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[Redsweater]

well three parts contribute to emotion:

intervals (minors, diminished blahblahlbha)
dynamics (loud, soft)
and rhythm (when you play adn when you dont)

a love song could have the same notes as a happy song, but the rhythm would make the difference for example. An angry song would have staccato rhythm while a grand song could have the same notes but let the notes ring. So in other words, find notes that fit, and just play it like you feel it should be played.

[Mike_E_McGee]

Some people start with a melody, and write chords later. Some write chords first, and then come up with a melody to fit the structure. Some people start with a poem (words???), and work from there. The thing is, a writer writes. The best practice you can get is to write a ton of songs. If your songs sound immature, that shows that you've got some writing to do. Just keep at it, and I'd start studying music theory pretty hard if I were you. Theory does not teach you how to write, but it can give you ideas of where to go when you write yourself into a corner.
I'd suggest music theory 1 from any college that is convenient. Once you've passed it, try theory 2, etc.
I went to Butler University in Indiana (USA) as a Music Theory/Composition major. I was shocked that the composition classes weren't really classes so much, as suggestions/assignments. One assignment I was given was to write a song called "Hoboken" for piano, using only the left hand. Okay?!? Not what I was expecting at all. The professor used assignments like this to get us thinking in different ways. Sometimes by restricting yourself (use only the left hand on piano) you open up new doors to your own compositional techniques. At the very least it was a good challenge, but I got much more out of learning theory.
To me, it was better to know about cadences, and secondary dominants and such. I could always find a reason to write a tune, but I needed to know about these musical devices in order to flesh out these composition assignments.
Overall, just stay with it. Having a keyboard at your disposal (hopefully with a built in sequencer) is one of the greatest compositional tools you could have. Stick with it, and work hard. I had to do everything in a practice room, across campus, on a piano (I don't play piano). It was tough, but one of the best things about taking a class on campus was that I actually heard my tune for Piano, Flute, and Basoon played by a pianist, and flautest, and a basoonist! Almost worth the tuition right there (too bad I dropped out before I actually got the degree (stay away from drugs...mmmmmkay?))
And don't be afraid of parallel octaves! Sure you lose a voice, but who says all the voices have to be completly independant? (I'll give you the answer....the theory prefessor will tell you that parallel octaves and parallel fiths are wrong. They are sinfull, and you'll be damned to an eternity sitting between brass players if you use them in one of your compositions)

Peace,
McGee