Learn a bit of theory, seriously a little will go a long way.
Open up FL studio. Open up FL keys. Set snap to grid half bar. Set the tempo to around 100 bpm.
Punch this into the piano roll
Move the third note down, listen to the difference. Move the third note back up and then move the second note down.
In the second bar I've just added some bass and higher notes in a higher octave.
You'll learn about the relationship between notes very early on if you picked up a bit of theory. I never wanted to pick up theory but even with just a hours worth of reading into the basics and you'll start to be able to make your songs sound better.
Or you can do what I and 90% of us did and try and figure it out on your own only to start to learn a bit of theory years down the line.