Well........

Some pointers:
- Throw in more of a variety of melodies
- Change the beat from time to time...
- It sounds a little empty, have something on the background, like a soft bass (sorry, but a bass does make a song full sometimes) or something else that just fills up the song.

Experiment. That's all I can say actually.
Diversity is the key for you I think ;)

(About the fullness of the song. I was coping with that in the beginning too, but I figured it out too.) ;)

2/5