I write most of the songs for my band... iba ibang technique, depending on what comes up first:
1.Lyrics first, music later:
When you have a string of words in your head, a great phrase, that would be good for a song, kahit just a chorus. I write it down first, then build the rest of the song around the main idea.
2. Music first, lyrics later:
Sometimes, while playing the guitar or practicing, I come up with a nice riff, or string of chord progressions. I do that first. Then write lyrics over it afterwards.
3. Simultatneous Lyrics and Music:
I think this works the best. While you are writing down the lines, try singing it and make the melody, then hanapin mo sa gitara or piano (whatever your instrument is)
Another tip:
Marami talagang writing styles, but I have one that makes it easier to make a song. The song does not have to be about you, you can write about other peoples experiences. Just think of a friend of yours, or someone you know... if he or she is having any problems in life, write a story about it, that can turn into a good song... you can make it fictional of course.