When hovering, or under shower, driving the car, or simply walking.

i improvise in my head (which i'm surprisingly good at doing) and when i get a part that sounds really good i jot it down in LSDJ or FLS as best I can

I smoke a real mang bleezy. grab my shit casio and jam out.  once I've come across something that I like I'll track it out and play around. then I build the bass around those melodies after placing some sketchpad drums. word.

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To be honest, my first writing experiences were literally putting random notes into a tracker. If they didn't sound horrible, I kept them.

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I bet it would be super frustrating using a tracker. I can barely use LSDJ anyway

I've had that feeling that my songs write themselves halfway through sometimes. I thought I was cheating/doing it wrong.

one note at a time?

I've never had the pleasure of tracking while high or drunk. I bet it's be pretty annoying though, what with my attention span already being that of a bottle-cap's

I thought you were being sarcastic and making an overwrought Michelangelo joke, but then I realized how great this advice actually is. Way to go. You really do have to let the song be itself at some point, and be a mature enough artist to let it do that instead of trying to bend it to a preconception of what a song is or should be. Kudos!

well i make sure not to touch the tracker until i've worked something out on keyboard. this doesn't always mean starting with a chord progression either, so much as looking for weird rhythmic clashes and quirks, or anything which slightly defies expectation. and after a certain amount of experience hunting for song ideas you'll start to gravitate naturally to comfortable ones, which is definitely a bad development, and you should try to resist doing your old stuff again.

my melodies still suck but you can't have everything

one way to find new stuff while jamming on an instrument is to do it while you're tired, because you'll mess up and miss chords and find stuff that might be new ground for you. i guess most people would have written "drugs" here

I just ram the keyboard and happy modules role out.

One of the most true things I have ever read.

I have a mega-shitty Yamaha PC-1000 keyboard sitting right beside my desk. There's no MIDI, no synth options - it's just a keyboard with cheesy stock sounds! But if I have an idea for something - or even if I feel like just messing about, I start jamming on the keys until I find something cool. I tweak it a bit, then once it sounds good I start writing it into FL (or Ableton, which I've been using more recently)  or track it onto LSDJ or Piggy, and go from there.
I sometimes find a pretty good chord progression, tweak it to sound good, then add a simple melody line. Although with the way my creative mind works it sometimes works backwards or in other directions. Just go with the flow!

I've been writing a tune in Music class on piano and guitar, then moving the chords to LSDJ. It's a very alien approach for me, but it's plenty fun!

I'm gonna echo what everyone else has said and say that if you're musically inclined in any instruments, just jam out on them. IF your instrument and music device both have midi in-out capabilities, maybe even hook them together and hear what it'd sound like in near-final form.
This cheap Yamaha keyboard is terrible for performance, but great for writing. I'd prefer using it to draft out melodies over the piano roll any day of the week!