Composition is awesome. Melodies are great. But the mix needs serious help, so let's talk about that!
=== MIXING 101 ===
Two big things:
* Internalize the following fact: 90% of mixing is getting volume levels to be right. There's no secret formula or magic technique - get the volume levels to be right and you're nearly done.
* Slots - You should consider your music as if it has a couple of slots: bass, midbass, midrange (melody/singing), pads, and high range. If you put one instrument in each slot, the song will sound totally full. But DON'T put more than one instrument in the same slot (unless you pan), because they will compete and mess with your song.
Alright, now for a step by step guide:
1. Go to the mixer in FL studio, go to the master channel, and remove any limiters you have. ALWAYS do this, until you get to the point where you consistently know what you're doing. They just make it harder to diagnose mixing issues.
2. Go to the loudest part in your song (1:20, I'd say). Make sure you're not in the red. If you are, turn down your volume levels until you aren't any more.
3. Turn down the master fader (the volume control that controls how loud the entire song is) until you can only hear a single instrument. That's your loudest instrument! Are you sure you want it to be your loudest instrument? If not, turn it down and turn up what should be the loudest (probably vocals in this song).
4. Turn up the volume to the point where you can hear every instrument, but just barely. It should still be very quiet. Now, set the volume levels for the whole song. Believe it or not, us humans make better mixing choices when music is really quiet. Why this is true is a long discussion, but this simple help will really help out.
Alright, I hope that helps. I'd encourage you to remix this song, it's good practice :) PM me if you have any specific questions.