I cannot say that I have much experience but the thing that works for me is that I don't do it alone. Usually, what happens is that we 're playing together (coguitarist and I) trying to find something interesting, a nice riff, some chords whatever sounds good (so music first for us).
Once we have a clue, we try to develop it trying to write down lyrics in the same time, but with a common theme or intent, meaning for instance to depict a character, a dream, an every day scene leading to a conclusion. The thing is, together we're not the most serious people, and it usually leads to hilarious songs, anyhow, try to find whatever inspires you most. The good thing to work in tandem, is that you get immediate feedback and sometimes, your partner will add something cool to the couple of notes or lyrics you 've started.
So, if you have a friend to work with, it could go very quickly: it takes us about 3/4 days to write a whole song, and then about a week or 2 to finalize it!

So, take your chance and have fun!