A great trap beat lives or dies on its melody. Here's a simple process for writing trap melodies in FL Studio that sound professional, even if you don't play piano.
Most dark trap uses minor scales: natural minor, harmonic minor (for that eerie raised 7th) or phrygian. In the piano roll, enable the scale highlighting so you only press notes that fit. Plugins with a scale lock, like Gambit's Lock to scale, make every note you play land in key automatically.
Write a simple 2- or 4-chord loop first (i - VI - III - VII is a classic). Then write your melody on top, putting chord tones on the strong beats. That's the secret to melodies that sound "right".
Trap melodies are often sparse and syncopated: short notes, gaps, a repeated motif with a small change at the end (A, A', A, B). Leave space for the vocalist.
Plugg and rage producers love fast arpeggios and bells. Hold a chord and arpeggiate it at 1/16 or 1/12 triplets, then add a ping-pong delay.
When you're stuck, a MIDI melody generator can break beat block. Gambit writes a whole hook from one held key, in key and on the grid, in Melody, Arp or Chords mode. Drag the MIDI straight into FL Studio's piano roll and edit it like your own.
Download the free trial and try Hold-to-play on your next beat.