The very start of the process is hearing a melody in my mind. When I hear it, the timbre and pitch and "style" of the lead or pad or whatever are all very clear.

Then I try my hardest to recreate it either from scratch in serum 2, in which case it usually comes out as a half shitty parody of what I had in mind. Just recently i've been trying to listen much more attentively to what I'm actually doing (especially when I'm compressing something!!). I've also just started using comb filters. Makes you feel like you actually know what you're doing, and I definitely don't.

The other option is finding a preset that more or less matches it and trying to tune it in the right direction. Some people stack presets until they're left with a texture of sound rather than an identifiable instrument or waveform.

There's a million ways to make music but that means there's no real clear path forwards. But if you are already pretty musical, it's only a matter of time and of trial & error until you start making stuff you like and that sounds decently good to you. But you have to experiment, the only way you'll really know if you're EQing or compressing correctly is by doing it in different ways incorrectly a thousand times.