I tend to write more about things that I am not so comfortable talking about. I find that you can never lie through a song and your lyrics will always come out much more honestly than you realize. Songs are audio snapshots of your life and it is important when writing lyrics you really express things in the most honest way and you open yourself up to that. I always find that I write much better than I speak, oddly.
Being a guitar player, I tend to start ideas on the guitar. There are times where I will encounter a situation in my life that I want to write about; and usually I have some guitar lick in my vocabulary that I can use with that. I tend to write the music first always. I than shape the lyrics and phrases around that. Something that always helps is to record your music first, and than practice singing and lyrics over it. That way you aren't burdened by trying to play in that moment, and you can focus on singing and writing. Than piece it all together in the end. Just remember to not get to crazy and write things you can't play and sing at the same time (I used to be very guilty of this.)
Follow your heart and the songs will come. Just never let a moment of inspiration pass.
Douglas Showalter