Before you start your song decide what key you want it to be in. Google 'notes in E minor' (or whatever key you want), then stick with those notes. When you're writing the song, if you feel that it sounds cool to incorporate an off-key note or two, go ahead.

On your track, I reckon there's gotta be a bit more melodic variation. It's just the one same melody through-out (granted you do some kind of staccato breakdown with it), towards the end I felt it getting a bit tedious.

Might be worth investigating how to create risers, as I feel this song would certainly benefit from their addition.

Also, add a bassline.