I've written few of my own songs. Many times I've got the inspiration from just trying out some weird chords after another. Sometime I find a nice riff this way and I write it down. When I got enough of these riff bits I try to combine them. Usually I write the chords in an application called band-in-a-box. Then I just browse the musical styles in the app and sometimes you get lucky and find a style which suits the song you're writing. From there it's just a matter of finalizing things in a multi tracker application and recording the tracks you need.

For example here's a weird combination of chords that could be molded into a bizarre jazzy song

(in 5/4 time) Em6 Em / F#m7 / Cm7 Bmaj7

A result of being too tired to do anything