Every song is different, but it always starts with the melody. I lay it out, along with a general idea of the "B Drop" (still the climax of the song but more melodic and not as crazy as the first half). For this, I just use presets for chords and bass and such. After I have it figured out, I work on making the sounds unique. I then move over to the A drop (screechy annoying skrillex turn-that-trash-down part), intro, and outro.
Most people mix and master after the process, but I prefer to do it all during. So after those bits are done, I keep adding sound effects, little "flairs", and sweeps. And then it's done!
Like I said, it's all different every time, but that's a general idea.