Write or hire someone to write the lyrics for your song if you have not already created them. If you don't have lyrics, look through poetry books with poems from authors that have been deceased for 70 years. These are in the public domain in most areas, but double-check with copyright laws. The Library of Congress website has information on copyrights for United States citizens.
Determine the form of the piece. A common form is 32-bar form in which there are four sections with eight bars in each section. The first section repeats, followed by a new, bridge section and then a return to the original section.
Choose a key signature for the piece. Using fewer flats and sharps will typically make the piece easier to play.
Write the first chord into your song. If you are in the key of C, the first chord should be a C major chord since C is the first scale degree. This helps to establish the home key; it is rare to start on a chord that is not the first chord of the key signature.
Create a chord starting on the fourth degree in the third measure and then move back to the chord starting on the first degree in the fourth measure. This will create a half cadence. A half cadence sounds less definite than a full cadence and is used in the middle of a phrase.
Place a chord starting on the fifth scale degree in the seventh measure. Even if it doesn't fit the key signature, make sure the chord is a major chord. The eighth measure should have a chord starting on the first scale degree.
Create a chord progression. When creating chord progressions, the most important thing is that there is a common tone between each chord. For example, a C major chord has the notes C, E and G, while a D major chord has the notes D, F-sharp and A. You wouldn't want to move from C to D because there are no common tones.
Use the chord progressions from the song to create quick riffs that accent the chords. For instance, if there is a C major chord on the first beat of a song, quickly strum the notes of the chord from bottom to top.