Learn the notes of the scale. For instance, the C scale has the notes C, D, E, F, G, A and B. Each of these notes can represent a chord.
Play rock and roll with the first, sixth minor, fourth and fifth major seventh chords. In our example, that would be the chords C, A minor, F and G7 played in that order.
Know that in the key of G, you would play the chords G, E minor, C and D7.
Practice playing this chord progression in different rhythms on your instrument until you are comfortable and competent in making the chord changes.
Start with having something to say. Some might call that an inspiration. Many songs are about love, in some form or other.
Try to keep your lyric lines similar in length and meter. Many rock songs are written in two or four-line stanzas.
Write three to five verses and a chorus for your song. The chorus can break out of the progression if you want to have a little change. The song "Runaround Sue" has a chorus that is not written in the same chord progression as the verses.
Begin playing the chords in the rhythm you want for your song.
Sing along with the chords. You may have to raise or lower your voice until you hit the correct starting note.
Continue singing and playing until you have worked out where all the chord changes come in the song.
Practice until you feel good about singing and playing the song.
Go out and become a star.