If by songs you actually mean full songs with lyrics etc, I don't.
I can't sing and I can't write lyrics.

On the instrument side, I have only written few tunes, so no pattern is evident. The starting point is almost always something that sounded cool as I was doodling and then I try to build up from it.

I have a way that works most often for me. I come up with a chord progression that sounds good and then just start singing. Sometimes I have an idea for words, other times whatever pops into my head. Then once ihave that basic skeleton of a song down I record it and then jam over the chord progressions trying to make the rhythm more interesting than just strummed chords.

When I'm composing music for work, what I'll do is close to ibz's method. Come up with an idea, and jam it out until I have a few parts. Then I record each part as a loop and try arranging the pieces until I have something that resembles a song, and then sometimes have to add connecting bits to make things flow a little better. Then I'll play it back and play along recording the new part and usually by then it's good for whatever I'm doing. When I'm working I have to get it done fast and this seems to be the most streamlined way for me to do it.

take this shit to electric

My songwriting usually starts with me noodling around on the guitar until I find a neat riff or progression, then trying to come up with a snippet of melody/words that fits it. Then I build around that. There are times when I've deviated from that, but it's generally much easier to make vocal/lyrics fit the guitar rather than the other way around.

that post didn't rhyme

-rep